The other half of Gauntlet and Rampart, obviously.
And, like Rampart, it’s an excellent conversion even on a very small screen. I did get stuck on Level 14 though – I had a pocket full of keys (© The Rock) but had to pick up another to progress. But I couldn’t. Thankfully, the old hang-around-for-a-few-minutes trick worked and the walls all turned to exits.