Curved cylinders

The best way I know is to use the 2D Shape Editor and rotate a hexagonal or octagonal (or more sides if you wish) shape created with it to the length you wish the tunnel section to be.

Its complex to try to explain properly but luckily there are a number of tutorials on this tool available so check the following sites collect all the tutorials on the Shape Editor and experiment with it till you get what you want. Once you have made the tunnel shapes you want they can be permanently saved for later use.
http://doe.lowlife.com/database/unreal/index.shtml http://www.unrealed.net/edtutes.phtml http://www.ozunreal.com/hosted/shade/index.html http://unreal.gamedesign.net/ http://www.ozunreal.com/tutorials/tutorials.html

My question is kinda similar. What's the best way to make an arched hallway, like the ones in CTF-Conquest's bases. Those are awesome! 2D Editor? Or can I just intersect half a cylinder with the floor? Thanks.

Both ways are suitable to build an arched hallway!

imo, i think it's easier to control the shape of the arch with the 2d editor. of course, it depends...intersecting can be a good option at times.

I think the 2d editor is way better. If you use an intersected tube you won't be able to make nice curvy corners for it...

At least, it's gonna be harder, way harder.