Cienfuegos has a different feel and character compared to other parts of Cuba. Their Malecon offers one of the most pleasant walks in all of the country, with it's calm seaside vibes and colonial French architecture. There are beautiful spots to explore outside of the city like the Jardin Botanico and El Nicho, and has some great and cheap diving opportunities. Consider extending your stay here to wander the surrounding area (via collectivo) and take it all in. This place truly is a gem in southern Cuba.
Situated on the southern coast of Cuba Cienfuegos is called "Pearl of the South" for it's beautiful, elegant French Colonial architectures. Wander around Plaza Jose Marti and Paseo El Prado to see the grand Colonial buildings as they bear witness to its glorious past. Arranged around a bay, the city has a charming waterside setting. The Malecon might not be as long as the one in Havana but it's as busy and lively in the evening with Cubans drinking and chatting the night away.
The city of Cienfuegos was once known as the "Pearl of the South" and the colonial architecture around the main square is still quite pretty. Tour the Tomas Terry Theater if you have a chance. Smaller than Havana, the dining options are a bit limited. Be sure to take a road trip to nearby Trinidad (about an hour away).
A nice place to stop if you are driving to Trinidad, but it did not seen like a destination in itself. Some very impressive buildings here.