I had an idea for a door which can be opened by someone standing on a heave inside the fort. I beleve however that the unfreezed door will be easy to remove by an engineer. too bad, but it works. Images:
http://www.enedahl.com/door/

This fort http://www.jyro.co.uk/phpAlbum_v0.3....castle/&var2=1

has 2 openable doors, made some time ago, but first working doors were in hmm... well i can remeber some from 1.4.2(one of the old released version of the mod, long time ago, before we had electricity and dev's had to code in candle light)

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But mine can be opened by anyone, not only an engineer. Just stand on the plank and the door opens.

And what happens if... lets say enemy tosses a nade over the wall, blowing the leveler block away?

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Yes that will blow it away. I told from the start that it wouldn't work in action. But it was fun building.

Back in 141 before blocks got froze in the transition between build and fight you used to be able to make pretty good sliding doors (and if you angled them right, not even someone with a grav gun could open them from outside) they were also pretty much immune to explosions.

I made that fort from eeros screenies :P

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Eat crayons, poop rainbows!

*COUGH* expect the door u made jumped off the rail when i tryed to open it, mine worked a bit better

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This is a clever idea - I would suggest putting your unfrozen slide-door inside your fort though, because unfrozen blocks are far weaker than frozen ones and are easily destroyed.

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It's 'Fik-Shus'

Good times, eh?
:P