The world of Game of Thrones is so vast that it can be difficult for casual viewers to keep all of the locations, characters, and religions straight. Although it wasn’t featured last season, Harrenhal is still a major location that’s important for viewers to going into season seven.

Viewers of the show most likely know Harrenhal as the Lannister army base in season two. The huge, ruinous castle was the backdrop for Jaqen H’ghar as he delivered on his promise to Arya to take three lives for her. It’s also where Arya served incognito as Tywin Lannister’s cupbearer, and the setting for Brienne versus the bear in season three.

However, there’s a lot of history behind the castle that you probably missed if you only watch the show and have never tackled George R.R. Martin’s A Song of Ice and Fire series. It was an important location during Robert’s Rebellion, and it might even hold a significant role in these last two seasons if some fan theories are correct. Curious? Here are 15 Things You Didn’t Know About Harrenhal.

Beware -- this article is dark and full of spoilers.

15. It’s the largest castle in the Seven Kingdoms

You might be surprised to learn that the Red Keep, the castle in King’s Landing, isn’t actually the largest castle on the continent. Although the Red Keep is the home of the Iron Throne, Harrenhal is both older and larger.

Construction of Harrenhal started decades before the Targaryens united Westeros under one crown. House Hoare, the rulers of the Iron Islands, decided that the rainy islands actually kind of sucked. (If only the Gryejoys were so wise.) King Harwyn Hoare ventured out and conquered the Trident and the Riverlands, the ancestral land of Catelyn Stark. Years later, one of his descendants would order the construction of Harrenhal. Since it was to be a monument to himself, he wanted the castle to dwarf every other structure in Westeros. Centuries later, his record still hasn’t been beaten.

The kitchens alone are as large as Winterfell’s great hall. Harrenhal’s great hall, meanwhile, was dubbed the Hall of the Hundred Hearths for its size -- even though it only has thirty-five hearths tops, it’s still big enough to entertain an entire army. The whole thing is better suited for giants than humans.

14. It lies to the north of the largest lake in Westeros

Fittingly, the largest castle on the continent also lies at the tip of the largest lake. The Gods Eye is named for its size -- when Arya sees it in A Clash of Kings, she realizes that she can’t even see a far shore. Think of it as a Great Lake in the middle of Westeros.

The lake itself also has a lot of history to it. In the middle of the lake is the Isle of Faces, where the Children of the Forest formed a pact with the First Men to end their war. The island is sacred and has one of the few godswoods in the south of Westeros. As the seasons change in Westeros (and as the violence grows even worse), the color of the water becomes grim. In the summertime, the waters are a beautiful blue and green that glimmer in the sunlight. During winter, however, the water looks more like steel.

13. It was named for its founder, Harren Hoare

To be sure that no one could forget which person ordered the construction of the monstrous Harrenhal, the castle is named for its founder -- King Harren Hoare, also known as Harren the Black or Black Harren. Harren Hoare was the last King of the Iron Islands, partially due to his construction of Harrenhal. We’ll get to that later.

He was hated by almost everyone because of how vain and cruel he was. His tactics were so awful that he gained a reputation throughout all of Westeros, not just the areas he ruled. Harren Hoare exhausted both the Riverlands and the Iron Islands to build his monument. Rather than paying people to build Harrenhal for him, he chained slaves to sledges or let them die in the stone quarries. When one slave died, they were replaced with a fresh body -- and on and on that went until construction was complete. Rumor has it there’s a lot of blood mixed in with the stone used to build Harrenhal.

12. It had a legendary godswood

The godswoods of Westeros are usually associated with the North and the Starks, who still worship the old gods. However, there used to be godswoods across the continent before they were either cut down or burnt by followers of the Seven. There are still a few in the south, and one of the most significant is on the Isle of Faces -- the island in the middle of the Gods Eye lake.

The godswood on the Isle of Faces covers twenty acres of land. This is especially impressive considering that Harren Hoare cut down many of the weirwood trees in order to build Harrenhal. Although the faces of most weirwood heart trees aren’t exactly pleasing to behold, the Harrenhal heart tree is terrifying. Its face is as cruel as the godswood’s former ruler, with a twisted face and glaring eyes. There are thirteen marks carved into it from a previous battle, and they still bleed every spring.

11. It was the center of the Hoares’ opposition to Aegon Targaryen

When Aegon the Conqueror first began his takeover of Westeros, Harren Hoare had just moved into the freshly completed Harrenhal. He laughed at Aegon when he showed up outside of the gates. He had just finished building a castle that no man or army could take down -- why should he be afraid of someone outside of his fortress?

He was partially right. There wasn’t a man or army who could defeat Harrenhal alone. But Harren Hoare had forgotten a pretty crucial detail: the Targaryens have dragons. Big ones.

The fire from Aegon’s dragon Balerion was strong enough to melt stone, and King Hoare was burned alive in Harrenhal along with his sons. The entire Hoare line was extinguished that day, and Aegon Targaryen became ruler of the Riverlands and Iron Islands simultaneously. The building has never been able to be repaired, and while it still stands, the entire structure is still partially melted from dragonfire.

10. Daemon Targaryen attacked it to kick off the Dance of Dragons

As if melting half of the building wasn’t enough, Harrenhal was attacked by the Targaryens again roughly 130 years later. This fortress can’t catch a break.

Prince Daemon Targaryen was one of the most skilled warriors in the Dance of Dragons, also known as Westeros’ civil war. He was both the uncle and husband of Rhaenyra Targaryen, whose claim to the throne he was ing. ( that Targaryen tendency towards incest? It’s not just the Lannister twins!) Since House Tully was sitting this war out, Prince Daemon figured that Harrenhal would be a great place to rally the troops. One problem with that -- the current lord of Harrenhal, Larys Strong, ed Rhaenyra’s opponent, Aegon II Targaryen.

All Prince Daemon had to do was fly his dragon to the top of the tallest tower. Lord Strong, ing how Harrenhal’s towers were melted in the first place, surrendered almost immediately. Easiest conquest ever.

Aegon II’s soldiers eventually retook Harrenhal, but no one is quite sure what happened to House Strong.

9. There are five towers, all with their own legends

The towers of Harrenhal are all distinctly named and have their own legends and lore to go with them. The original names were lost after Aegon’s dragon burned Harrenhal to a crisp, but the five names that persist in the Game of Thrones world we know are the Tower of Dread, Widow’s Tower, Wailing Tower, Tower of Ghosts, and Kingspyre Tower.

The names make it slightly easy to guess the history or rumors that accompany each tower. Kingspyre Tower, for example, is where Harren Hoare died when his fortress burned. The successive lords or castellans of Harrenhal have lived there since. A stone bridge connects it to Widow’s Tower, underneath of which is a huge cell for prisoners. The Wailing Tower is named for the noise you hear when the wind blows from the north. The Freys lived here after Roose Bolton reclaimed the castle.

The Tower of Dread is where the northmen were held prisoner, while the Tower of Ghosts is closest to the sept and the most ruined of the five towers.

8. It took 40 years to build

It’s either funny or tragic that the famous ruins originally took forty years to build. Given the building’s size and the physical limitations of the people constructing it, this time frame makes sense. After all, its stables alone can fit a thousand horses, and its curtain walls are apparently roughly as tall as a mountain cliff.

After all of the tragedy and pain that went into building it in the first place, House Hoare didn’t even get to enjoy it in its intended state. The very day that Harren Hoare moved into his cavernous new home, Aegon Targaryen came knocking at the door with dragons. Hoare literally had less than a full day to live in his fortress. Given that only a third of Harrenhal is occupied at once due to the cost it takes to maintain it, we can guess that he only actually saw a tiny portion of what took forty years to create.

7. People believe it’s cursed

The constant tragedy that afflicts Harrenhal has given it a reputation in superstitious Westeros. People now believe that the whole place is cursed, and for good reason.

Countless numbers of people died while Harrenhal was being constructed, and some say that Harren Hoare mixed their blood into the mortar. There's literal blood in the walls of the fortress, and that never bodes well. Many say that the whole place is haunted, especially the Tower of Ghosts. There are a few stories in particular that are told frequently that the Stark children learned from Old Nan. Mad Lady Lothston was said to send a giant bat to snatch children for her pot. Others claim that the ghosts of Black Harren and his sons still walk the halls, with the flames that killed them surrounding their silhouettes. Meanwhile, some servants go to sleep and are never seen or heard from again.

To make matters worse, no one can seem to keep a hold of the place.

6. It’s been held by more than six different houses

After House Hoare was destroyed, the Targaryens didn’t keep Harrenhal. While the dragons settled in at King’s Landing, House Qoherys was granted Westeros’ largest fortress. House Qoherys held it for thirty-seven years before Harren the Red, who claimed to be Black Harren’s lost grandson, took it back. It was short-lived -- as soon as he had killed all of the men in the castle and named himself lord, he went back to being a bandit.

Harrenhal would later be held by Houses Harroway, Towers, Strong, and Lothston. In keeping with the rumors of the curse, each house died out a few generations after claiming Harrenhal.

No one seems to be able to hold it for long, not without some sort of tragedy befalling them. Since 298 AC (the beginning of Game of Thrones), Harrenhal has been held by nine different individuals. Even for wartime, that’s a lot of turnover for a massive castle.