I love caving. I remember one particularly tough horizontal tube crawl. It was probably 50 meters long and about 200cm wide and 150 cm tall. If you weighed more than about 100 kilos you would likely be stuck. Crawling consisted of one arm out in front, the other was down at your hip, pulling with the lead hand and pushing with the trailing hand and toe tips. At the half way point there was a rock dipping down from the ceiling, requiring some back and hip arching to get past. At the far end was a small triangular room at about a 60 degree tilt, with just enough room for 3 of us to stand in. Good times!