In this article, we describe a newly-invented chess variant called Switch-Side Chain-Chess that is demonstrably more challenging for humans and computers than the standard, international version of the game. A new rule states that players have the choice to switch sides with each other if a continuous link of pieces is created on the board. This simple rule increases significantly the complexity of chess, as perceived by the players, but not the actual size of its game tree. The new variant therefore more easily allows board game researchers to focus on the 'higher level' aspects of intelligence such as perception and intuition without being constrained by a larger search space as they would be if using a game like Go or Arimaa. They can also immediately build upon the tried and tested approaches already being used in strong chess engines instead of having to start from scratch or a lower level of progress as is the case with other games of this type.