Hobbies And Interests
Starting the Quest
There's no point in using the secret passage to visit the vampire of Castle Skingrad unless you're trying to complete the Lost Histories quest. This quest comes from the Thieves Guild, so you'll need to be a member first. Starting the quest requires you to sell at least 400 gold pieces worth of stolen goods, and then talk to the Khajiit named S'Krivva that lives in Bravil.
Following the Trail
Work through the beginning of the quest by talking to some beggars in Bravil and visiting the castle in Skingrad to get a job by speaking with Shum gro-Yarug, the castle butler. At this point you'll gain access to the dungeons where the prisoners are kept. Speaking to the prisoners and following the trail of blood left on the floor will lead you to find the secret passage to confront the vampires. Without taking the job you won't be able to get into the cell where the trail of blood begins.
Secret Passage
Although the mysterious trail of blood takes you through a small tunnel, this isn't the secret passage. You'll emerge in the wine cellars of the castle where the real secret passage is hidden. When the trail of blood ends at the wine cask, look for a candle mounted on the way. Activating this candle by pressing "A" on the Xbox 360 or the space bar on the PC version opens the door to the hidden tunnel.
Problems
It's possible for you to enter the secret passage in the wine cellar before beginning the Lost Histories quest or entering the cells of the prisoners. However, opening up that tunnel before the quest starts can cause problems. The vampire hidden within, the Pale Lady, plays an important role in the quest. She'll attack you as soon as you open the passage. If you kill her at that point, completing the quest is possible but requires extra work.