Miramar is a stretch of beach on the Pacific coast of Nicaragua, about an hour's drive from Managua. It's one of the least frequented beaches - you definitely won't find the tourist crowds that you do at San Juan del Sur, but you won't find many Nicaraguans, either - which means it's clean, quiet, and relaxing. It's also located on a sort of inlet, meaning the water is calmer and warmer than at most of the other Pacific beaches. It's the perfect spot for a Pacific-coast, palm-tree-lined sunset.
Spend a few days doing nothing but relaxing in Miramar by renting a beach house (many of the homeowners live and work in Managua, and rent out their houses when they're not using them) or renting a room from a local. Or if you want to learn to surf (Miramar's a great place to learn, as the water is fairly calm), there are a couple small hotels in the area that offer classes geared toward beginners.