[Radek]

Only one thing to add: The Teleport spell will teleport you to the (right) portal on the same map. Therefore, if you are in a dungeon, then the Teleport spell will teleport you to your portal inside that dungeon. If you are in the wilderness, then the Teleport spell will teleoprt you to your portal in the wilderness. And so on. The Teleport spell cannot teleport you from one map to another.
Therefore, if you are about to investigate some dungeon, then:
1. Create a portal at the entrance to the dungeon (in the wilderness). You'll be able to teleport there after leaving a town.
2. Enter the dungeon and create a portal at the exit from the dungeon (inside the dungeon). You'll be able to teleport there from anywhere in the dungeon.
Now, you can travel to and fro freely.
1. Teleport to your portal near the exit of the dungeon, click the lever, and cast Call of Home. You are in the town.
2. Leave the town and teleport to your portal near the entrance to the dungeon. Click the lever. You are back in the dungeon.