Questionaut is an online video game from the BBC where players have to answer questions related to English, Science and Math. As you answer the questions correctly, a little “questionaut” in a balloon gets to continue on his journey.
It’s accessible to Intermediate English Language Learners.
I’ve placed the link on my Intermediate English page under Word and Video Games. You can find the “Walkthrough” there, too. You might also want to read an article I’ve written about how to use these kinds of games as language development activities.