What are some "must Knows" for winter Urban Exploring?

I would usually treat it similarly to regular Urbex, as once you're inside of a structure it won't really matter. But, one thing to know is that you will create footprints in the snow. This isn't huge, but owners and others may be prompted to check cameras and increase security. That and just winter being cold, so obviously dress warm in case you need to spend time outside.

Depending on what you do and the conditions, some doors and stuff may be frozen shut. But inversely, you can use the conditions to your advantage. Coming from Wisconsin where the winters are usually pretty harsh, no one will want to be outside, so your chances of being spotted are lower. Especially on cold or snowy nights. But then again I have no idea where you come from, so this could change drastically.

If you are into draining as well, granted that the snow isn't melting and temps are below freezing, this is a time that I see fit for draining. This is because there is low risk of flooding during these time periods. There probably more but that's all I could think of for now.

Wear a coat.

mostly just prepare for the cold lol

Keep some of those "hot hands" packets in your coat pockets!

Wool socks and thermals. Dress in layers, and shed them as needed if you start sweating. If you stop moving and are sweaty, you'll get cold awful fast. If you carry a pack, throw some extra socks in there in case you get wet feet somehow. I also always carry at least 2 methods to start fire, dry tinder, a couple emergency blankets, and a few protein bars just because you never know - you might get stuck/trapped or you may run into someone in need. Water. People all too often forget to hydrate when it's cold.

A lot of abandoned buildings have flooded lower levels. These will often freeze in low temperatures and let you explore areas that aren’t normally accessible. Just be careful that the ice is thick enough to hold your weight.

I don't know if it is true but wet buildings seem less sturdy to me. Like they are turning into clay or like an overchewed icecream stick.

It's pretty much like summer urbex, but colder and with visible footprints.

winter sucks. stay inside. drink hot cocoa and bitch about winter online to anyone that will listen.
works for me.

I explore all year long but if you enjoy exploring drains in the winter like I do then that's great. I highly recommend it because in the winter, when it's very cold outside, you can walk on the ice to get into drain outfalls and there are times where I will see some nice ice formations in the tunnels as well as smooth ice in the outfall that goes reasonably far before the ice starts turning into water for which by then the water won't always be deeper than your boots but I got to be careful when walking on the ice because the ice can be dangerously slippery if I'm not careful walking. As of the winter of the 2023-2024 year, I like winter more than summer for exploring drains because it doesn't rain and it's a very nice experience when I come out of a manhole cover while it's snowing and there is a lot of sparkling snow all around me plus it being cold adds more excitement to the adventure! I also love it when it's windy on top of all of the cold blowing (drifting) snow. I didn't originally like to explore drains in the winter at first until some of my friends showed me the goodness of winter drain exploring.

I will also say that I always wear many layers of clothes whenever I explore, walk etc for safety reasons but I am hot blooded so wearing excessive clothes might make me more hotter than is necessary but I still wear about 5 layers (upper) and 3 layers (lower)just in case something happens. Every once in a while I get the chills (LOL). I've been known to go outside on walks in below 0 temperatures (wind chill advisories to be exact). I've had times where I've explored drains when it was 30 below 0 with blowing snow. One of the drains was a 3 foot RCP tunnel but half of the outfall had snow drifting over it and it had ice throughout the tunnel. On top of that it was very cold and windy plus it a 30 below wind chill advisory. This experience made me feel like I was crawling into an igloo and that was what I call an arctic adventure. It was fun times too.