knowitall has got it all right, so a mega thanks to him.
ill just try and tutorialise it abit
By sexing up the walls and adding butresses i mean this

Notice how the hallway isnt just bare and boring like it would usually be. It looks great, and very good looking. It may only seem like a small step, but i truly makes maps looks so much better.
Also notice that the pic on the left, uses simpler techniques and is just blocks. Yet it looks brilliant.
To do this, first decide where it going to go (on a wall or in a hallway) then just get your basic block, which is the right height and thickness, then fiddle with it, and to make it into a couple of different pieces, doing this by resizing then cloning.
Then just make it into a butress looking thing
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^^ that one uses three different pieces, the bold one, the one ontop of the bold one, and the one below. BTW that butress is from the view of the above screens, so there would be one on either side
the highest bit is just a thick block. The lowest bit is just a thin bit. Then the bold bit is the bit that slant to make the two meet up. Incase you dont know, you slant something by using the clipper tool.
It doesnt have to be like that, its just and example, but it should give you the idea. Obviously they would be spaced out evenly, and be on either side of the room or hallway.

the left is kind of what your current map is. the right is a much improved version, that removes the "box map" feel
1.) notice the slants on the wall. They take 2 seconds to do, but remove the boxy feel, make things look more interesting and are good for bases. A theyre easy to add to existing walls.
2.) THE PIPE! Right, first off, his pipe curves, you do not need that. I have been mapping for quite a while, and curving pipes baffles me. You can just make a straight pipe. Also the dark grey supports on the pipe are not needed at this stage, so dont worry about them.
to make a pipe.
1.) make a square brush, then go to Curves>cylinder then it will turn int a cyclinder.
2.) Get it the right way round, then just resize it to fit the gap.
3.) In knowitalls map, his curves around that sticky out bit, you can just have it going into the sticky out bit, and then coming out the other side, It'll look good and is alot easier than the hassle of curving it around
4.) when you texture the pipe, if it looks stretched, shift click the cylinder to higlight it. Then hit S, a window called the surface inspector will come up (the pne we used to resize the textures previously) then just click on "natural" and the texture should no longer look stretched
Also in the screen you'll notice the sticky out bit running along the top. It is simple, but make the room so much more smexy (alot like the butresses.) and they are another one of the super easy things to do. Just make the block, and your done! They dont have to be as big as knowitalls, you can have them thinner, but it will look smexy nevertheless. Also instead of it being a block you can make is a cylinder isntead
Hes got mini butresses aswell in the doorway, it makes it look smexy!
the bits of floor missing i dont paticularly like, but i think thats just me :S its pretty easy to do if ya want to but... i preder boxes and stuff.
thats pretty much it. If you dont understand my instructions feel free to ask.
thanks again to knowitall for providing such great screenies