I haven’t used an iPhone in years, but Mike Anderson over at Code Fellows says that if you own an iPhone, it keeps a map of where you’ve been and a log of how long you were there. If he is correct, you can find it by following this path on your iPhone:
Preferences > Privacy > Location Services > System Services > Frequent Locations > History.
And, yes; he says you can turn it off. Get all the juicy details at Code Fellows