I'm kind of learning this language on Duolingo, and I am wondering if this language is useful.
Saluton kaj bonvenon al Esperantujo!
Anywhere where you can find a Pasporta Servo host, essentially an Esperanto-speaking couchsurfing host. I have heard many good things about Brazil, Iran, France, Sweden, Germany...
A good place to travel is Berlin, which has seven Esperanto clubs. There's always something happening in Esperanto Berlin.
I don't know of any places that have such a high amount of Esperanto speakers that you can ask a random person in the street something in Esperanto, unless there is an Esperanto event happening there.
Travel to an Esperanto event, make some friends and you can travel all over the world to meet them again.
I don’t think there is any one particular country that Esperanto will help you visit, but instead you can use it to travel to Esperanto events around the world. The events have their own culture and interesting people, so you can think of it as like a travelling country that you can visit anywhere!
Some of the major events for Esperanto speakers are:
Or if you are in Europe then these are really worth visiting:
Of course most countries have their own local events too.
The thing about Esperanto is that enough people speak it so that if you know where to look, you can find speakers in nearly any moderately populated area. On the other hand, few enough people speak it that when you find them they're really really excited to meet you.
But for Esperanto in the US, the Northeast is where it's at! (See link.)
In the Northeast US, on the weekend of June 3 - June 4 the best place to travel to is New York State where there will be a Senkrokodila Semajnfino: Novjorkia Kampado.
There will be a guided hike to Kaaterskill Falls on one day, and another to the mountains around the campsite on the next day. The campground has amenities to fill the rest of the time kaj certe ni Esperantumu.