What is a spider burrow?

It is a tunnel or shaft dug into the soil. It can be lined with spider silk. Trapdoor Spiders make a "door" for their tunnel out of their own silk. Some burrows consist of one straight shaft. Other burrows are constructed like the letter H with one door visible from the outside, and the other exit not quite dug through to the outside until an emergency exit is needed. There can be an inside door protecting the horizontal tunnel. If the spider is attacked by something that comes inside, the spider will retreat through the second door, close it behind her, and hope that the intruder will go all the way to the bottom in a straight line, be unable to find anything to eat, and will then leave. If that does not work and the intruder pulls open the inside door, then the spider retreats and exits by digging out the top of the hidden vertical shaft.