Yea teleportation really breaks immersion. I would honestly remove it all together. Traveling into the Underdark should be like an expedition. Be prepared or die not just tp out half way.
Unless stuff "respawns", its pointless to have to walk through cleared rooms manually. When your character goes on a journey you dont narrate it round by round. You move along until something interests you, rather than say "I ride my horse forward. I ride my horse forward this round too!".
Temple of Elemental Evil was AWFUL with no quick travel. It just ate your time to walk through floors where you've wiped out all the enemies.
