Is a Wormhole a tunnel? In films such as Interstellar, 2001: A Space Odyssey, and Contact (and also Star Trek Deep Space Nine) wormholes are depicted as tunnels along the edges of which fantastical colours and shapes lie. For example, this is a picture from 2001:



What would passing through a wormhole be really like though?
A wormhole, or Einstein-Rosen bridge, is inherently unstable. It will collapse before anything can traverse it. Keeping it stable enough for even a photon to get through requires negative energy densities. And that requires exotic and suspicious new physics in most cases. Technically there are well-known effects which can produce negative energy densities, such as the Casimir effect. But being able to harness such an effect to stabilize a wormhole is beyond current technology (to say nothing of creating the wormhole in the first place). We have no observational evidence to suggest wormholes exist, especially not on the scales you see in Sci-Fi.

So in the rapidly collapsing case it looks like nothing except possibly a spray of subatomic particles (which you might not even know aren't the usual background ones), and in the stable case it's impossible to say because you'd have to know what the exotic matter or other negative densities look like.

As for what it's like to traverse a stable wormhole, as long as the exotic matter doesn't mess with you then it would be pretty much the same as any other spaceship travel. You could just have interesting time travel effects and beat light rays that went around the wormhole. A number of these are mentioned on the wiki page.