[Radek]

Entering dungeons is a bit nonstandard in W&W. You will always (with one exception) find a closed door in a "transition room" and a lever somehwere near the door. When you click the lever, the game will load the dungeon and you will occur in the same room but with the entrance closed and the door, closed so far, open. Also, you will see another lever at the same place where you have clicked the lever.
You are now in the dungeon. When you want to leave the dungeon, click the lever in the "tansition room" inside the dungeon. The game will load the exterior, the door leading into the dungeon closes and the door out of the dungeon opens. That's all.

Notes:
1. The only exception mentioned above is the Stout Mines dungeon. There is no lever there. The "lever" is a jester sitting behind the bars. "Clicking the lever" is "giving him the Writ". He will give you the Writ back so that you can leave the dungeon giving him the Writ again and so on.
2. Note that there are two "transition rooms": one belonging to the exterior and one belonging to the dungeon. After gaining the teleportation spells, you can place a portal in the "transition room from the exterior" so that you can teleport to the dungeon from everywhere in the exterior and another portal in the "transition room from the dungeon" so that you can teleport to the exit from everywhere in the dungeon.