>>9530616Humans constructed the pyramids and the tower of Babel with stone and simple tools.
Also note that constructing large structures under water is easier, because things dont weight so much there and can easier be transported and constructed with. And if you need to repair something on the roof, you simply swim up, there is no need to construct stairs or any such things. Plus, unlike on land, the higher you go, the easier it will be to build, because the pressure of water gets less and less. So creating mega structures larger than anything on earth might be completely possible without and sophisticated technologies. Just by putting stone over stone (more or less).
Plus, if we assume that the sea aliens have tentacles, then you could actually build much better and quicker with them, than with human arms and fingers, because you would have more of them, you could grab things tighter, reach further, etc. Their tools and buildings would probably look much different from ours.
If they need a water-tight space to make experiments in, that can be done. They could also achieve an airtight space under water, e.g. a vacuum chamber.
All in all, there is no reason to assume a civilization cant develop under water.
