V-Ups or V Sit-Ups are a great exercise for both higher and lower abs. Not easy to do and thats why it works.

Few links on how to do it:
https://youtu.be/AJD6aPu5kw4
https://youtu.be/riAutegDqdI
https://youtu.be/SX8eFytsVfI
https://youtu.be/iP2fjvG0g3w