If you've never been stranded in a foreign city with a dire need to find a public restroom as a direct result of the previous night's curry, you've never truly travelled. And this is what makes Layar a necessary travel companion - it will show you not just where the public toilets are, but a heap of relevant information superimposed over the real world, to help you find what you need wherever you are.
Layar is an augmented reality app. Even better, it's a free augmented reality app. But it's strength lies not in the fact that it doesn't just cater to one kind of augmented reality purpose - it is a platform for multiple types of augmented reality apps.
For example - if you need to find an ATM quickly and easily, and using an ATM finding app might confuse you because you can't read maps. Layar has an ATM option that will point you in the direction of the surrounding ATMs. There's the aforementioned Public toilets map, restaurant maps... the list is endless.
For the most part, the key layers for the app are free, but there are also paid options. For the most part - let's not mince words - the different layers are useless bundles of poo. But for the layers that are actually good, this app deserves to belong on your iPhone.