Subway Surfers wrote:
Situps and lots of them
Leg raises of all kinds work better than situps, develop the butt muscles too, and pose less injury risk.
Just lie on your back and lift and lower your legs (under control) over and over again.
Throw in some bodyweight squats if you need to round things out.
If what you want is cosmetically appealing abs, then you have to run a lot, maybe 100kmw, depending on your body type, because you need low body fat to look all ripped.