I had to take my helmet off to get through comfortably. Pretty close quarters. It took 3 years for a group of 3 cavers to dig it out. They had to haul the dirt out of the cave. When they first found it, it was only a few "inches" high. It looked like it went somewhere, so they spent the time to dig is out and it paid off. That's the thing about caving....you might come across a small opening and not think it goes anywhere, when it actually opens up to a another huge section of cave. It takes a long time to first survey a cave, because of having to check out every potential lead.