Nicaragua... Corn Islands in the Caribbean are amazing! Isla de Ometepe in Lake Nicaragua is unique, Laguna Apoyo, Volcan Mombacho, any local festivals, Granada, etc. etc. Lots of great culture, scenery, food...

If you want to discovered nicaragua go and mixed with them and you will learn a lot!!..people are very friendly and happy even that they had 15 years of civil war....go 2 corn islands which is in the caribbean in nicaragua you can find the contracts of caribean and pacific on the caribbean corn island,blufield is amazing plus they speak a mix of english with their own language sumting like jamaican language!...if you go to the pacific go to isla de ometepe,granada,leon....beautiful countrie plenty volcanoes! you will enjy it but you have to be careful!! any where in latin-america you go you always have to watch out for criminals but you will havthe most amazing experience in your life!

If you go to Costa Rica make sure you see Volcano Arenal, Go to the hot springs near the volcano, and visit Cahutia on the Caribbean side

tortuguero in costa rica is amazing.. and the pazific side..white and black beaches...great! if you want some adventure go to monteverde, rainforest, there is a parc in the forest, where you can fly through it with rops.. it's called canopy tour..really funny! the arenal volcano is also a good place, there are some hot springs, heated by the volcano..nice to relax.! hope i could help you a bit!

For Nicaragua : vianica.com

If you want to discovered nicaragua go and mixed with them and you will learn a lot!!..people are very friendly and happy even that they had 15 years of civil war....go 2 corn islands which is in the caribbean in nicaragua you can find the contracts of caribean and pacific on the caribbean corn island,blufield is amazing plus they speak a mix of english with their own language sumting like jamaican language!...if you go to the pacific go to isla de ometepe,granada,leon....beautiful countrie plenty volcanoes! you will enjy it but you have to be careful!! any where in latin-america you go you always have to watch out for criminals but you will havthe most amazing experience in your life!

Most of these answers are good, and I completely agree with D.G.

Lots to see in Costa Rica -> Manuel Antonio, Arenal/Tabacon Springs, some of the smaller beach towns in Guanacaste. In Nicaragua -> Granada, Omeptepe Island... I haven't seen Corn Islands but really want to... I found on a ride up from Costa Rica to Nicaragua, we had to spend 2 hours at the border. So, there may be some delays there if you're driving from Costa Rica to Nicaragua.

well, Nicaragua is very poor due to 15 year of civil war, plus bad governemnts. But people are nice and there is plenty to see, maybe more than in Costa Rica since it has not been exploited. Great hiking in volcanos, beaches everywhere. Cheap! places you can go... Leon,matagalpa(selva negra),Granada(mombacho volcano,isletas,isla de ometepe),Rivas(san juan del sur). Corn island on the atlantic, but transport is very dificult to that region.

Nicaragua - check out Granada, Leon, Omeptepe Island. Costa Rica check out Monteverde, Arenal / La Fortuna, Tortuguero, Puerto Viejo and Manuel Antonio. San Jose isn't the best of cities in my opinion. Corcovado park in Costa Rica is really secluded if you are interested in wildlife.

I haven't been to Nicaragua...yet, but there's so much to see in Costa Rica. Manuel Antonio is suppose to be gorgeous and I always miss it when I go. Tamarindo was kind of a dusty surfer town...kind of cool, but not the prettiest. There are some very nice beaches close by though. Just north of Tamarindo is a beach made of seashells! Hope that helps a little.