Solentiname Islands is in Nicaragua on the southeastern corner of Lago Nicaragua.
The Solentiname Archipelago is in the south of the Nicaragua Lake near San Carlos in the Rio San Juan Region. The islands are really remote - don't expect things like grocery stores movie theaters etc. On the Isla Mancarrón is a little Pulperia with the most necessary stuff. There are 36 islands but just a handful are inhabited. The biggest Islands are Manacrrón and San Fernando.
The only way onto the islands are via boat. Private boats can be chartered for around US$100 per day. Otherwise collective boats leave from a pier in San Carlos near the current construction along the seawall. The schedule is San Carlos to Solentiname Tuesday and Friday 1pm for C$80 and returning the same days at 4:30am for the same price. You might be lucky and find someone from the island running around in San Carlos and giving you a ride to the islands. A good place to ask about boats leaving for the islands is MiniCyber Ortega or the alcaldia.
There is no motorized traffic and you should be able to walk anywhere you want. Transport between the islands is only possible by boat, and as there are hardly any public boats, it will cost you unless you can get a small group together.
There is still some intact nature on the islands even though the people do farm the land. There are also petroglyphs on the islands.
On Mancarrón you can visit the church that Ernesto Cardenal built, Nuestra Senora de Solentiname. He sometimes goes there to preach, but you would need time or luck to catch that. The church itself is a charming and colorful building inspired by his misa campesina (peasant's mass), which is still sometimes held there.
Visit the museums on the main islands.
Some of the hotels have a restaurant as well that also serves outside guests. If you self cater, there are a couple of small ventas with a limited selection. Most likely you will eat at your hotel anyway.
There are no worries about safety on these small islands. There used to be bull sharks in Lake Nicaragua and the Rio San Juan, but unsustainable hunting has all but exterminated them, making pollution your bigger concern when swimming.