The Dragon's Keep was Dragon's home before she abandoned it.
In the first film, Shrek wants to get the banished fairy tale characters out of his swamp. Meanwhile, Lord Farquaad, who rules Duloc, plans to finish building his kingdom by getting a queen to rule beside him. When he starts a tournament to find his knight to appoint for facing the dangerous dragon, he lost all his men to one ogre which he names the knight for his quest. Shrek accepts in return that he gets his swamp back from the occupying fairy tale characters. Shrek and Donkey try to sneak to the tower where Fiona waits, but Donkey awakens the dragon. When Shrek tries to save Donkey from the dragon, he is tossed up into the tower. Once he rescues the princess, he must find and take back his "noble steed". They succeed in fleeing the tower where they nearly fell into a pit filled with lava.
In the second film, the abandoned castle would become unoccupied except for Big Bad Wolf when Prince Charming finally arrives to save the princess. The wolf informs Charming that Fiona is already rescued and married. In this movie and later ones, the castle would be frequently mentioned sometimes where Shrek wished he never rescued Fiona.
In the fourth film, Shrek finds himself someone who no longer exists. In order to reverse the deal that took away his life, he has to get his true love's kiss, meaning Fiona. He ran to the Dragon's Keep, which was abandoned, even though Donkey was never there to get Dragon to find him. It is revealed that Fiona escaped herself and had grown tired of waiting (which she thinks will never happen).
The Dragon's Keep looks like a ruined castle. It is surrounded by a pit of lava, and the only way to get across is to cross a rickety bridge. It also has a lot of towers; Fiona's tower is the tallest. The bridge fell apart in Shrek. However, in Shrek 2, Prince Charming gets across, and he went to rescue Fiona. However, he realized that the Big Bad Wolf had taken her place while reading a magazine.
Inside the highest room in the tallest tower is where Princess Fiona lived (one could say, "Slept," but it's revealed in Shrek the Musical that she is actually a "morning person", and usually drinks a lot of coffee every morning) until Shrek rescued her. The room is relatively simple, round, carpeted walls, and a window-seatName? that opens up and doubles as a chest.
Dragon's Chambers include the Treasure Room, the Bedroom, and the extra chamber. Dragon's Chambers haven't got use as Dragon abandoned it.