https://www.wired.com/story/how-much-time-to-dig-an-underground-pool/

This is a pretty cool video. This guy starts with just a simple tool and digs a giant hole in the ground. From this hole, he makes a small swimming pool and a little underground room. But damn—how long would it take to make this? The video is only 20 minutes long, but surely it must take much longer than that to build the pool-house thingy.