Learn Hardcore Russian: На морском курорте мы долго слушали прибой вечером. - At the seaside resort, we listened to the surf for a long time in the evening.

Russian often uses на with places that are thought of as sites, venues, or destinations where an activity happens, and курорт is commonly one of them.

So на курорте is the normal way to say at a resort.

на морском курорте = at a seaside resort
в would usually suggest being inside something, and with курорт that is not the usual choice.

This is something you largely learn as a collocation:

на курорте
на вокзале
на почте

while other locations take в, such as:

в городе
в гостинице
в доме

Why do both морском and курорте have those endings?