I can second rock climbing, whether outdoors or inside. Its format is addictive. I also found tennis very easy to fall into. On the opposite end, there's runnin

I can second rock climbing, whether outdoors or inside. Its format is addictive. I also found tennis very easy to fall into. On the opposite end, there's running and swimming. They feel like misery for me personally. Others find them easy to do routinely. Just have to find what works for the individual. There are sports out there that won't feel like a chore.