I'm using the exercise bike to build endurance

Since I can't run every day, I'm using the exercise bike to build endurance as well. However, the problem is that it gets pretty boring. I can do 30 minutes on the exercise bike (generator powered where you must keep the speed up to where it's about 20mph effort no matter what "hills" are thrown at you). After 30 minutes, I start getting really bored and it doesn't help that since I'm not outside, the sweating gets really bad too. But mostly it's boredom.

I've tried the radio, and sometimes it makes me go too fast but eventually I even get bored of that. I can't hear audio books over the sound of the exercise bike. I used to sit and ride it and think about papers I was writing and stuff like that when I was in school, but now I don't have to think about that type of stuff anymore.

So what motivates you to stay on the exercise bike? Do you play silly games or solve math problems in your head? I want to get up to at least a 3 hour endurance level eventually. Right now I can do an hour.