Some more pictures that can be used as adventure settings. These were taken at Lost River Gorge & Boulder Caves in North Woodstock, New Hampshire. It is a 3/4 mile hike down and then up a gorge. Along the way up are various side caves you can enter. You should be able to click on the pictures for a larger view.
These are some of the entrances into the side caves. For perspective the 3rd and 4th picture are the same shot, with the 3rd picture showing someone crawling in.