Under water structures
 

So I'm wandering around Frontier and find quite a few underwater 'palaces' - usually with glass roofs.

How are they built? How is the water 'excavated'? Were these mountains at one time, next to the 'sea', and then constructed under the seabed?

How deep underwater?

Several meyods mine use sand and either doors signs or fences to create air pockets

the method I have seen most is that of setting up the outer boundry, placing down the glass roof and then filling with sand and mining the sand out - horrible way to spend time :D

Deep.

And yes, filling and excavating does work but surely not. Some underground buidings on frontier are massive, and deep. And fantastic.

Could put a boundary around an area then pump water out??

If you start with a glass roof, then place sand blocks directly beneath it won't they fall down, destroying any water blocks they pass? That way you only have to place and remove one level of sand and not fill the entire volume.

The sand does inded fall down, but im not certain it destroys all the water - just the one it occupies. In other words, the water flows around the sand as it falls, destroying the last block of water on the seabed, allowing excavation, one block at a time.

I shall try it none the less. :)

You need to totally fill it with sand, then dig it all out once you have your walls up. If you place a couple of doors on the floor of the ocean its a great way to move around while being able to breath.

A helmet of respiration is great to stay underwater for much longer.

There are some great examples of underwater construction in Hunger City, like the subway.

When building underwater i like to do a small section at a time and it quickly becomes a nice size building.

Had this been the FTB server you could have used a filler to fill it all up, and then the same filler to clear it afterwards. But it isn't, so that's not an option :p