San Carlos is a city in Rio San Juan department of Nicaragua.
San Carlos is a local transportation hub. That doesn't mean there is a lot going on but if you travel the region you can't miss San Carlos. In November 2009 the municipality inaugurated the brand new Malecon which gave a needed face-lift to the city.
There are daily flights from Managua (~US$120 round trip)
It's a small city - everything is in walking distance.