I have got 2 hollow cubes ( rooms)lined up. Is it possible to cut a doorway out between them. I can't see a carve tool?

its called csg subtract.

Got it. Thanks

is probably better to not use cgs subtract.

I have found just using blocks to build your level the best wihout
using subtract.
You "build" your openings as you need them.

It's a *really* good idea NOT to use cgs subtract. There's a high probability that using it will result in any number of invalid artifacts being left behind that will screw up your level come compile-time. I made the mistake of using this "feature" when I first got 3DGS, and I built my entire level using it often, and then discovered what a mess it had made and I had to rebuild everything again.
I wish they'd just remove the feature altogether so others don't make the same mistake (especially if they haven't checked the forums here first)...

Use csg substract if you need it, just be carefull. Take also care that there aren´t any blocks overlapping in your levels.

No dont let them disable CSG Subtract, its so usefull for cutting shapes directly out of blocks like arched doors, round windows, etc...
Just use it with care and only if you need to for doorways (personlly as suggested above, build the doorways block by block)

LOL!

Well, maybe they could at least nerf it in some way, so that 3DGS newbies (like I was) don't mistakenly use it all over the place, only to discover later on that they'll have to rebuild everything in order to fix all the errors. Or some kind of pop-up warning, etc. I really REALLY wished at the time that I had read the forum first before using this feature, but then logically I would have had to know that it could be a problem first, which is unlikely for a newbie. Anyway, up-front cautionary advice would be helpful.

I remember taking 3 days to clean up my first mess with that ...function but thanks to Dan, found a way to use it when needed and just brushed the rest together.
Hunting down blocks was a nightmare untill I discovered that if they were involved in a group, the group had to be opened to locate the offending artifacts.

Hollow block should be used with care too, take the time to get the size right before commiting the hollow command or if you need to resize, rebuild then re-hollow as more probs can crop up when scaling a hollow block unconstrained.

In theory they all work fine...untill you compile and then the engine decides to add more to the mess untill you select 'dont snap vertices' but then...more probs as the subtract might end up looking good with this option but other blocks decide to play up and so on add infinitum!

So now I hand build doorways, window and the like (oddly enough, most other users dont get the results I get and vice versa...strange)