No they dont usually. The casinos and the shops all close too. But sometimes it is very nice to just be amoung just a few who stay on ship. Use the pools with few people and deck chairs are in abundance too. I have come back from a excursion early and it was quite heavenly. Just enjoy each others company. Happy cruising.... Char
Actually, you may find some activities scheduled on NCL during port days. Not as numerous as on sea days, but there are usually some quiet things going on... movies, exercise classes, tea, and so on. Of course the spa is open and there are usually discounts on the treatments on port days.
NCL doesn't necessarily close the children's centers on port days. If you want your children enrolled on a port day, you must sign up by 8pm--it's considered "group babysitting" and there is a charge.