A hole for an indoor swim spa?

[Bancroft]

In Africa in my youth, we often had garden pools that were only half underground.  Basically, if you want a 2m deep pool, dig down 1m then use the soil you've removed and bank it up above ground to make up the other metre.

 

Worked really well and might, I imagine, help with keeping costs down, avoiding a lot of reinforcing, and reducing the amount of water-proofing required for a fully dug out pool.