I agree that "crotch area" sounds a bit goofy. Just "from neck to crotch" or "from neck to groin" would be better I think. Also agree with Faktablad's last critique.
He found that the caves in the rock formation were larger than the cramped entrances led you to believe. He found a suitable one that’s entrance he had to crawl with his belly on the ground to enter. One disadvantage was that the sound of the oncoming march reverberated throughout the cave, and was quite distracting. He took off his robes and put it at the mouth of the cave. He then reached into an inside pocket in which resided a few matches and a striker. He then chastised himself for not collecting wood and kindling. He felt around for his robes again and he pulled them off the entrance way.
At the end of this paragraph you begin four sentences in a row with 'He'. And before that you had two in a row. Too repititive. Very distracting. Other paragraphs are probably making too much use of 'he' as well.
Other than that, sounds interesting.