Found a strange hatch in the basement - WHAT is this?

[andersfrick]

In the space under the stairs leading to the basement in the 1960s house, there is a white-painted hatch fastened with four screws. When I unscrew the hatch, I find... well, what? Neither I nor the previous homeowner has any idea what this is. It looks like a box (electrical?) that has then had some cement over it, presumably in connection with a major renovation done in the 1970s. In the rest of the space, there's only incoming water, about 3 meters away from this hatch.

WHAT is this?

 

[Stefan N]

Looks like a cleaning hatch for the drain.

 

[andersfrick]

Looks like a cleanout for the drain.

Aha! A bit difficult to clean the drain then…

 

[cpalm]

Aha! A bit difficult to clean the drain in that case…

You might have to chip away some cement to get the lid off, but that's probably quickly fixed if needed.
But it has undeniably never needed to be used 🙂