There's more than meets the eye in Hrodulf's House in Skyrim: Dragonborn
Opening a Trapdoor leads you to a mysterious larger area underneath the house
See the Hrodulf's House Secret Trapdoor tutorial below to find it:
Furthermore, within this hidden zone there is yet ANOTHER secret area, accessible by activating the Bookshelf
The bookshelves are actually a Secret Door that reveals a Hidden Passage behind it.
See the bookshelf tutorial guide below for help. The screenshots show you which bookshelf to activate and the tunnel that's behind it:
