I think the Monte is the most recognisable and so its retrograde equivalent, there are more but usually so heavily modified they can't be recognised as the things in themselves anymore. I'll do like my awful math teachers and "leave the exercise for the listener". But really, what stroke me was the idea that direction and functionality are based on simple patterns and not some abstract root movement.
A lot of Ligeti's etudes can be quite challenging at first because of the high virtuosic energy, like Chopin doing jazz on drugs. My favourite is actually very accessible, the dreamy Cordes à vide. After listening to the etudes you can go to the full Piano Concerto.