Begging to differ, I don't see where weight lifting, pilates, yoga differ from cycling in terms of building bone strength, as they equally do not have "impact".

It definitely builds muscle. hell yes. They won't pump up as much - they will first get lean and efficient - and of course it will be limited to your legs - but you build calorie-burning meat.

maybe for the bones, MTB'ing would do it. Or riding cobblestones.