ABANDONED. children/YA SciFi Boys find spaceship in cave

[Citatel]

I have read book (book series?) sometimes after 1975 in Slovakia (so this doesn't have to be English writing author). This was what hooked me on SciFi and reading in general. I want to get this book for my daughter, but, obviously ;-), I do not remember the name or author.

Three(?) boys find an old alien spaceship in a cave. At first they just play around then they find out the proximity of spaceship helps them to learn homework. There is scene where they examine a map of world (or an atlas?) in proximity of the ship and afterwards they can find any town on a map, frustrating geography teacher that takes great pleasure making kids look for obscure towns on map.

Later they boys visit some planets and have great adventures there.

[Ann aka Iftcan]

NO idea what this book is Citatel--but if its been translated into English (or even started live out in English) I definately want it for my YA/children's sci-fi shelf.

[Lobstergirl, au gratin]

Citatel, are you still looking for this book?

[Lobstergirl, au gratin]

No response, moving to Abandoned.