From Costa Rica to Nicaragua

[Britt]

Hello,

in May I'm going to Central America for one month. I will fly to San Jose, but want to see a piece of Nicaragua first. I think I'll take one week to do that and want to travel by bus.
I'm curious what your advises are to see in Nicaragua and what the best route can be for one week? How can I travel best from San Jose to Nicaragua and is the bus save enough to travel with? Which places are 'must-sees' and which can I skip?

Well, I hope you'll understand it, I'm Dutch !

Greetz,
Britt.