800m runner... sprained ankle. training?

Pool workouts like aqua running - look it up. Most running-specific cross training.

I actually don't have regular access to a pool...

I looked around and found some people talking about a stationary bike? Even though it doesn't work the same muscles as running does, it'll keep my aerobic systems up..?

Weights. Isolation weights. Pool.

Sucks, do it.

Join a gym with a pool. The weight area will be useful too once you get healthy again. As for the ankle, take it easy. They can take a long time to heal up, unfortunately. "traumatic" injuries suck.

The stationary bike is a great idea if you can do high intensity training. You can also use this as an opportunity to focus on core strength.