From the Brick Experiment Channel, here’s a home made submarine with LEGOs, complete with a minifigure. More details from Brick Experiment Channel:
This RC sub has magnetic couplings to transmit torque through the walls. No need to drill holes = no leaks. At the end I test it in a swimming pool. Enjoy!
Source: https://blog.adafruit.com/2020/07/07/diy-glass-submarine-with-lego-and-neodymium-magnets/