What could be more cool than sleeping in the bottom of a volcano.  That is what you can do on the Crater of the Moon National Monument's Wilderness Trail.  Sleep in the bottom of Echo Crater.  To backpack and camp in the wilderness area requires a free backcountry permit.  It is a little more than 3 miles of  backpacking to the crater,  the last bit is off trail so you will need the map provided for the area.  Access to the crater is from the east side of the crater, access the crater from any of the other sides is faster but it will be your last as it is a several hundred foot vertical drop to the bottom.  No water sources so you will need to pack at least a gallon of water per person per day.  Make sure you use the vault toilet at the trailhead before heading out, if you need to due #2 you will need to back all of it out, and that's more than just the paper.  No digging a hole and burying it here.  Plenty of flat ground to pitch your tent in the bottom of the crater.