Removable bridges are loved by some and hated by others. I have one across a three foot door, which gained me another 20 linear feet of wall space, so it was definitely worth it.
There are a number of different ways to build them. Some engineering will definitely be in order, but to me, that is half the fun of model railroading! I took a very simple approach, and have a truss and girder bridge supported internally by a steel channel. The area across the door isn't scenicked or anything, just the bridge going across.
Now, just so you know, my layout is nowhere near complete, but I have used the bridge with some of my preliminary track plans that I laid out on my foam, and it worked great.
There is a thread here on the Gauge showing the bridge, I'll see if I can post a link. Also, others may have suggestions on how to build the bridge, and may have way better ideas than mine.