Veendam cruise? Besides aerobics [forget that]--but I'll definitely do the marathon walk.
Do they have perhaps some arts n craft classes? Or how to design a webpage? Any tech classes?
No. The main components of cruising are eating and shore excursions (and drinking, for some people). (and gambling and onboard shopping if you get really bored.)+ live evening shows.
There MIGHT be a cooking demonstration by the head chef. Maybe a beginner dance class. A free movie every day (on some ships) - but you are expected to find the lighter things you want to do. (Trivia contests, go swimming on board, drink and dance at night, find your photos on the wall (and they hope you buy some), start conversations with other people, piano bar for relaxing, a small library, internet access at a cost, - you are even on your own for walking around the deck.)
It is an enjoyable and worthwhile trip and adventure. Have fun!