To the right side, of the light on the left hand side, at the bottom of the pool, in the first picture. It also looks like that whole panel may move.
This looks like a hose and and a drain.
Rinse it down the drain.
Likely not used as a "pool" as another anon pointed out. And look closely at the bottom line of the panel where the drain appears to be. Does that look like a watertight seal?