Essaouira is a coastal town three hours from Marrakech. Visitors can travel there via direct busses with Supratours or CTM or more adventurous travelers can take a cheaper and somewhat speedier grand taxi. Read more about traveling via grand taxis here. Essaouira is known for its traditional gnawa music scene and the sound of gnawa's Afro-Moroccan reggae style music often provides a backdrop to strolls through the white- and blue-walled medina streets. The city hosts an annual gnawa festival in June of every year that is attended by tourists and Moroccans alike who come to listen to local and world renowned musicians.
Jimi Hendrix was very taken by Essaouira and there are famous, yet erroneous, claims that he wrote "Castles Made of Sand" after being inspired by the sight of an old Portuguese castle that has succumbed to the ocean sands in the shallows off of Essaouira's beaches. Not true, but the castle is an interesting reminder of all the colonial influences that ruled over Morocco.
Not far from the ramparts and the beaches is Essaouira's functioning shipyard where fisherman display the catches of the day and boat builders are hard at work building and repairing massive, sea-faring boats.
From Essaouira, you might continue your journeys further south to the pristine beaches of Sidi Ifni, which is a small Amazigh coastal town with breathtaking landscapes an top notch surf.
Tiny little Portuguese fortress town south of Casablanca, which makes for a great day trip if you have the time. One of the main sites to see is a cistern built in the 1500s that was featured in Orson Welles' Othello.
A complex city, known for its historic place in Western literary cannon from the likes of William Burroughs and Paul Bowles, Tangiers also happens to be the border city between Morocco and Spain, or more broadly, between all of Africa and Europe, with a mere 9 miles separating the two countries. Most Moroccans in the north speak Spanish as their second language. Because of its proximity to Spain, drinking and tapas culture is a bit more accepted. If your travels take you through Tangier, get mint tea and besara soup at Hafa Cafe. Go to the Kasbah and the museum of the Kasbah. Check out the excellently curated Ligation Museum. Go to the Cinemetheque in the heart of town to catch a movie or to get a sense of the cultural undercurrents; the Cinemetheque is a great Moroccan-run space that is transforming that part of downtown Tangiers.
Between Tangiers and Rabat is the coastal town of Asilah that is known for its beaches. There may be better beaches along the Mediterranean coast or south of Essaouira near Sidi Ifni, but I always liked going to Asilah because of its proximity to Rabat.