Truing a twisted (vandalised) wheel/rim Overnight someone stamped on my wheels, hard enough also to bend a pretty substantial rear rack. (Not a great welcome to Copenhagen, my lights were stolen last week...) Neither wheel would turn more than 1/4 turn before jamming against the mudguards. 

I laid each on a parking bay's "L" corner, and gently stood on them, which has made them true enough that they spin freely in the frame.

The disc brake pads are fine, and the frame and dérailleur look undamaged.

Is it realistic to true wheels after damage like this? I'm guessing it's beyond the skill of someone new to wheel repair.
Sorry to hear someone vandalized your bicycle. I've been a bike mechanic in the past and there is a point of no return for rims in my opinion. This issue is that point can be subjective based on bike use and needed quality. From this point on, the wheel will tend to come out of true easier due to the weakened rim. Interesting, what you did by stepping on the rim I've seen done at shops and recommended in how-to videos. You can get a spoke nipple wrench and improve the rim by truing between the brake pads. Grep "how to true bike wheel" on Google for a start. I've seen side-to-side improve a bit in extreme cases but up/down hops will be harder to get out. If you do take the self-serve option remember use little corrections at first. Also, attempt to keep all spoke tensions even. Taking it to a shop is an option but labor plus and parts will be a chunk of cash towards a new wheel at the end you'll still have a wheel on a rebuilt rim. Finally I don't know how the bike shops are in your area, I would give you a free assessment if you came to mine. After all this, if the wheel refuses to stay in true sorry but it would be replacement time.