I recently added a room puzzle to my current game and the players really responded to it. They said it freaked them out. Essentially, there were two mirrors in the room. Both reflected the room but the one reflected the room while also showing an item on the table. When the players looked at the real table, it was not there. The puzzle requires them to bring the two mirrors together to create the 'portal' for them to travel into to get the item. The reflected room does not lead anywhere else because it only reflects the room and not places outside the room.
The portal idea comes from one of those haunted house shows that say the most haunted house in the country has dark wispy beings leaking out when two mirrors are placed facing each other. When the player's characters entered the reflected room, they suffered an unusual amount of vertigo and walking was extremely difficult because they could not see the actual floor, but only the reflection of the floor. Spot Hidden checks, Dexterity checks, Sanity checks, were all used as well as an Idea roll in case they did not know of the mirror myth. Hope this helps.