Climb up the mountain. Use X to jump. You can climb walls with the Up key. You can also wall-jump if you press X while not pressing Up.
There are no lethal obstacles, but you will die if you fall more than four blocks' distance then hit the ground. But if you grab a wall instead of hitting the ground, you will survive.
You can place up to three respawn points at locations of your choosing.
* This comic.
* Bolo's so-called Little Green Man.