Dead Castle was a castle on an Dennaskar. It was formerly the seat of government for the populace for the planet. However, following the depopulation of the world, the Imperials took over the building making it an Imperial base. At some point before the Battle of Endor, Tay Vanis crash-landed on the world in his X-wing starfighter. After being captured, Darth Vader came to the planet and tortured the man into a persistent vegetative state.
Vader then placed the man into a small locked room, informing only the only local troops of Vanis' location. To the rest of the Imperials, Vader let them think that Vanis was still on the loose for his own purposes. With the false information, the Dark Lord was able to keep several of his more aggressive officers busy, as well as keeping many Rebel agents out of the way as they searched for a man that was already in the Imperial's possession. Vader placed an Imperial officer in charge of the castle and placed a prerecorded hologram near the door of the small locked room to taunt anyone that was able to find the planet where Vanis had crashed.
Around 3 ABY, Luke Skywalker, Leia Organa, and C-3PO came to the world and infiltrated the castle, discovering Vanis' comatose body. Vanis' droid LE-914 self-destructed near her master, killing them both. As the Rebels left the castle, Skywalker sabotaged the buildings main power station. As they departed in the Millennium Falcon, the castle exploded, making a lasting monument to the Rebel spy.