When I was going to London as a tourist, we only paid for an international data plan on my wifes phone. I then found this offline map and downloaded it thinking it may be of minor usefulness. Boy was I wrong. This app kept being the most useful thing we could have. It allowed me to search for sites we knew the name of but had no clue where they were. It let me plan out our day so we got the full benefit from each time. And having access to the undergrounds map only made it that much more useful. Most days I ended up using more battery than my wife because we were always using this app. And we both have the same iPhone. I would highly recommend this app for anyone who wants to make the most of a trip to London.