Agadir is the main sea resort of Morocco. The city was primarily developed after a terrible earthquake destroyed the city in the sixties. The city follows an occidental design, and very little of the old Moroccan quarters remain to date.
New resorts are built all the time and new clubs and casinos abound, so make sure to ask fellow backpackers or the staff at your Agadir hostel for the popular ones, since here is not much worse than sitting in an empty club listening to old tunes from the nineties. Agadir is an all-season resort town, but it tends to be crowded with locals during summer school breaks, and not really warm enough to take a dip in the ocean in winter (but still much warmer than most of European resorts).
Agadir is not too hot in summer, and it can offer a great break from the heat you will generally experience in Morocco, just a few kilometers inland. Agadir also has a massive fishing harbor, famous for its sardines. If you want to taste the local food, there are many small restaurants which offer basic but very fresh seafood dishes, such as shrimp, grilled sardines, and fish tagines. These small restaurants tend to be very cheap, which is a rarity for Agadir where the prices of things are similar to Europe.
Inland from your Agadir hostel, there are many opportunities for hiking addicts, and north and south of Agadir there are plenty of surfing and windsurfing spots which can be easily reached by public transportation. The staff at your hostel in Agadir will be able to help you sort out which bus to take. There are also Agadir hostels which are actually in the near vicinity either on the coast or the mountains, so choose based on your main interests.