Duplicants cannot reach certain spots in my base / Pathfinding

Dupes movement is limited in liquid.

So okay, is this a bug or a weird feature?

Dupes without exosuit wont pass through water > 2 Tiles. Thats normal. 

You can build some ladders unter the water to let them move in it without exosuits.

Thanks for the clarification, it doesn't feel intuitive though and is never mentioned. Especially because sometimes dupes will do stupid things like going into a high pressure or extrem heat area without a suit and that's a thing they should not.