In this paper we introduce the prototype of a cognitive training environment called “Merobrixx”. Merobrixx is a serious game for players of all ages, including children and elderly people, based on traditional mental rotation training methods. Players interact with the game by means of a Tangible User Interface (TUI), which consists of three-dimensional objects made of LEGO bricks. A first evaluation of the system confirms that the user’s performance in the game is positively related to his or her general mental rotation ability. Based on these findings further research regarding the conditions for a long term training effect is planned.