Question: So, as I've mentioned in previous questions, I am writing a series in which the four young main characters encounter natural, traversable wormholes that connect the present time to another one. I've vaguely figured how I want them to work and how this way connects (mostly) to the real theoretical science behind it (specifics will be explained below for those curious and if it connects to my question). My question now is this; If I want to continue being vaguely scientifically accurate, how would a speculative wormhole look to humans looking at it from outside? For someone stepping through it to the other side? How many artistic liberties can I really take while still being scientifically accurate? Thanks so much for taking the time to speculatively answer this question and have a good day!

(For those interested, the wormholes tend to stick near objects with larger gravity to keep our intrepid little explorers from stepping through one and ending up somewhere out in space and suffocating. They tend to occur most on the time equivalent of "fault lines" where time 'tears' more easily, like weak points on a blanket. Yes, I do know it's definitely more complicated than that, but I'm simplifying things a bit so it makes more sense. They also can connect places in both place and time, so they can end up from a little town in modern day Oklahoma to the volcanic jungles of Early Cretaceous China. Finally, they are also traversable by simply stepping through since the main characters are just a few teenagers who stumble across them and don't exactly have resources to get a vessel to take them through Interestellar style.)

Answer: 
Wormholes are purely hypothetical, but would probably appear similar to a black hole. Take a look at the artistic interpretation of a black hole, from the movie Interstellar [here](http://interstellarfilm.wikia.com/wiki/Gargantua), and that of a wormhole [here](https://en.wikipedia.org/wiki/Wormhole).
My postulations:  

1. What the wormhole looks like depends on how light interacts with it/ passes through it.  

2. If matter can pass through it trivially (i.e. simply stepping through with no ill-effect), light should act in very much the same way.  

3. As mentioned by others, a wormhole is simply a 3D hole (most likely spherical).

In this case, I would imagine that the "look" of a wormhole will be surprisingly simple - in fact you would not see it at all! All you would see is a circular view of the destination the wormhole connects to, with no distortion, refraction (disregarding differences in air pressure on either side), etc. It would actually look a lot like an open door, except without a door or a frame. 

The peculiarity would only show when you tried to walk around it - the hole will remain a perfect circle no matter how you tried to walk around it, and what you saw in it would be a 360-degree view of what was on the other side. Imagine if you had a wormhole from your current location to the inside of a museum, for instance - by just walking around the wormhole you would be able to see the entirety of the museum's displays.