The Extension Building brings more possibilities and fun to the GraviTrax railway. The Extension Building contains many different basic components for extending the marble run. Combined with any GraviTrax starter set, the Extension Building brings even more variety and ball fun to the GraviTrax universe. How much longer can the ball roll with the new elements? The Extension Building brings completely new possibilities to the GraviTrax tracks with 29 exciting basic parts. Thanks to the versatile elements, even longer GraviTrax tracks can be built and ball tracks can be discovered for even more ball action.