I found a lovely book in Oxfam the other day.
It's rather tackily put together with a fake leather binding made of red plastic, and didn't look very promising. But when I opened it, I was fascinated.
The book has colour photos of modern Rome, but plastic overlays allow you to see how the buildings would have looked in the time of, say, Julius Caesar, Vespasian, or Constantine. They're rather poorly done, in fact, but what a great idea - seeing Rome as the Romans did.
I'd love to work on a programme for putting translucent visualisations on an iPod. That would be a fascinating way to walk around Rome. It's so difficult to make lumps of rock come to life, but this little book did it.
And it only cost £1.75.