If you see your hometown as a capture-the-flag game just waiting to happen, then Google's Ingress might be for you. Having built up its player base on Android, the augmented reality game is available now for free on the App Store for iPad and iPhone.
The alternate reality world of Ingress is fought between two teams that you can align with, namely The Enlightened and The Resistance. The two parties are vying for energy sources locked within real-life locations, and so it's up to you to find these sources with your mobile in hand. By jetting around town you can capture locations, unearth energy, build up skills, and co-ordinate larger-scale virtual assaults with other players.
With Ingress, you'll never need to look up from your phone during those boring museum visits and dreary sightseeing trips with loved ones. To check it out, head to the App Store.