San Juan Del Sur, a beach area in SW Nicaragua known for its surf, north and south of town, a gringo haven, and not a very pretty one at that IMO. For beach time, consider near Leon.
You might want to break the trip into areas, if there is one advantage to renting a car, it would be to explore the north, and most fly to Corn Islands, and you dont need a car for the Ometepe>Solemtiname Islands, Rio San Juan portion, its all boats. Paxeos and taxi hire for the rest.
Get the MOON Nicaragua book, you will be set.
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