info teleport destination
From Quake Wiki
This entity is used in almost all levels, as destination points for trigger_teleport entities. You need to give this entity a "targetname" keyvalue to connect it with the trigger_teleport's "target". The facing direction is used to define the direction the player is facing after teleporting. Download a teleporter example map by clicking here.
Several teleporters can address the same destination with no problem. For example, no matter which skill gate you step through in Quake's start map, you always end up in the same location in the episode selection room. Although these entities can't be used with difficulty settings, with some advanced mapping, you can make certain teleporters only available at certain skill levels with a func_wall or something along those lines. This will allow you to put teleporters (ie: needed to access the next area in the map) that are open at higher skill levels on terrain that is difficult to reach, and possibly at ground level, in plain view, for the easy skill.