The Temple of the Elders level spawns with a special teleporter. There are two options at a divine teleporter.
You have the option to play a previous level and farm more items, or continue to the next level, Risk of Rain (Level).
For those confused by which key to press to activate which option, the "Use" key that activates teleporters will "Loop" players back to the first level. Every level henceforth will have a divine teleporter and allow this same option, moving players through normal levels (with significantly increased difficulty) in the same order as the first run through the game. The "Alternate Use" key which swaps On Use items will activate the final level.