(the image isn't my basement, its a random image I found at trigearlab) I have a treadmill and a bike set up in my basement for the upcoming winter. Those long runs and rides are a special type of torture when you don't have anything to focus on for the multiple hours of activity.
For me personally, I've started getting into virtual rides on youtube. I'll connect my computer laptop to my monitor and run the workout recording through my laptop and youtube through my larger monitor. I'm also very specific on what I enjoy. It needs to be road biking (I can't get mentally into mountain or gravel biking videos) and I prefer it to be near the Mediterranean coast. Beautiful climbs are also interesting, but I'm not as into other backdrops. I've also tried watching live sports, but that tends to impact my heart rate in ways I don't like.
So what do you like to do to keep yourself occupied while running or biking indoors?
I think I commented in the cross post, but will put here too:
I use rouvy (recently acquired by zwift ☹️) for a lot of my winter riding, having real video for all of the routes is way nicer. There are lots of group rides/races you can join if that's your thing. My cycling club even runs a club winter league on there!
If I'm doing long rides, i tend to put on some podcasts to listen to.