Castle Dour

Located in Solitude,  serves as outpost to the Imperial Legion during the Skyrim Civil War. General Tullius resides within, along with his second in command, Legate Rikke. Both command the Imperial forces in Skyrim.

Castle Dour Dungeon
The Castle Dour Dungeon is the dungeon inside of Castle Dour. Those who commit crimes in Solitude are sent here to serve their sentence. There Is also a escape shadow mark marking a wall that can collapse.

Emperor's Tower
The Emperor's Tower is a wing of Castle Dour, reserved for the Emperor of Tamriel, when he visits Skyrim's capital, Solitude. Lavishly furnished, the tower contains many valuable items. The Solitude Windmill is connected to this wing.

This is the location for the Dark Brotherhood quest "To Kill an Empire", and to prevent the quest to be spoiled in any way, the tower is a lock-out. The front door at the castle courtyard is locked and the lock cannot be picked, while the backdoor at the bridge to the windmill isn't, but that doesn't matter.

When getting inside the interior, one will end up in a very small room with another locked door. The front door will be unlocked after the quest, but that door will only unlock during the quest events and will never unlock again, if not using console commands on PC.

Quests
Battle for Solitude Siding with the Stormcloaks during the Skyrim Civil War, the Dragonborn sacks the tower with their fellow Stormcloaks, as their final plan mobilization about the Imperial Legion.

Breaching Security
Gaius Maro is scheduled to patrol Emperor's Tower and Castle Dour, day and night, on Morndas', surveying the area for suspicious activity before Emperor Titus Mede II's arrival in Skyrim aboard The Katariah. The Listener of the Dark Brotherhood might have executed him in one of these two locations and planted an Incriminating Letter on his corpse, as a warning to Commander Maro.

To Kill an Empire
Impersonating the Gourmet, the Listener of the Dark Brotherhood plans to assassinate Emperor Titus Mede II. The Emperor visits Skyrim to attend to the business of the civil war, as it is believed that his cousin, Vittoria Vici, was assassinated due to the conflict.

However, this was incorrect as she was executed by a member of the Dark Brotherhood. He resided within Castle Dour and the Listener, disguised as the Gourmet, slipped the fatally poisonous Jarrin Root into his stew. Receiving a tip from Astrid that an assassin was coming to kill the Emperor, Commander Maro replaced the Emperor with a decoy who was killed instead. As the Listener tried to flee the Castle, agents of the Penitus Oculatus intercepted them, failing to remove the Dark Brotherhood member who subsequently escaped.

Trivia

 * The castle is one of two faction headquarters that is not marked as a fast-travelable landmark, the other being Jorrvaskr, of the Companions.
 * One of the cells (usually the only one with a lock lower than Master level) in the lowest level of the Dungeon has an "Escape" Shadowmark on the floor. Inspecting the wall above said Shadowmark reveals Crumbling Mortar on the wall, which can be activated to destroy it and open up a passage. This leads into a forgotten tunnel, containing a Steel weapon on the floor (usually a dagger), and leading through the other side of the hole visible from the room with the Evidence and Prisoner Belongings chests. The tunnel ends at a ladder leading up to the Dwemer-looking sewer opening in front of The Winking Skeever. Tested with both and  installed. Sometimes due to a bug the wall will not collapse.

Bugs

 * When exiting the dungeon after serving time you might be immediately attacked by a troll. This is dangerous for low level characters as the cause is not yet known.
 * Paying off a bounty will result in you being placed outside Castle Dour, minus any stolen equipment. It is possible for a single unusual enemy to spawn right outside with you, including: a Frostbite Spider, a Falmer or a Troll. This is one instance a Falmer can be found on the surface world but it is assumed to be a bug.

Schloss Elend Castillo Severo Мрачный замок