On my way to Copàn through Nicaragua and Honduras I have visited the cities of Riva, Ometepe, Granada and Leon. Crossing Nicaragua is an adventure in itself mainly because of the untouched landscapes and beautiful nature.
The summit of Volcano Concepción (1610 m) is evidence of its active state. The volcano is the second highest and one of the most perfectly shaped volcanoes of the Americas; however, it is a safe place by European standards and with respect to other volcanoes.
Ometepe actually consists of two islands joined by a narrow isthmus 2 miles (3 km) in length, it emerges from the the Cocibolca, the great Lake of Nicaragua. The island is a mesmerizing place, entrenched in history, and full of stunning sights and activities. The island’s land is fertile and largely forested; coffee and tobacco are the principal products. Alta Gracia and Moyogalpa are the island’s main towns.
Past Indian inhabitants regarded it as their promised land and a sacred island. Chorotega, Nahuatl and Mayans left a multitude of pre-Columbian artifacts spread all over the island. Due to the many petroglyphs and stone idols carved into basalt boulders Ometepe is considered one of the great rock art areas of the world.
I suggest you to make Granada your base because transport, accommodation, and food are cheaper; additionally, locals will easily arrange you small wildlife trips during transfers.
Go to San Juan del Sur beach town in one day and come back to Managua. This trip is perfect to get relaxed at a private beach, get tanned under the sun, lay down over the sand and take unique panoramic pictures at "El Cristo". San Juan del Sur is well known as one of the best beach town environments made out by restaurants, bars, and tropical music
If you are a history lover, León is your place to explore in one day. León city was once the capital of Nicaragua and today is one of the most important cities in the country. It has 2 World Heritage by UNESCO, the largest Cathedral of Central America, active volcanoes, the first university of the country and more.