The Magic FM promotion, created and planned by UM London, runs until Friday, building up daily to the Drive Time show hosted by Angie Greaves. It will be supported throughout the day on air and through Magic FM's website.
A different London location or landmark will feature on air each day of the competition, with three clues broadcast through the day to help listeners identify what it is.
Listeners will be encouraged to look on the Microsoft-owned Multimap site and win prizes including Michael Jackson tickets, a K West weekend spa break and personal shopping experience, and a wine-tasting tour at Vinopolis.
Clues will be broadcast on Neil Fox's More Music Breakfast Show, Gary Vincent's Test of Time morning show and Paul Phear's Magic Afternoon show designed to drive listeners to search on Multimap. The winner will be revealed on Greaves' Drive Time afternoon show.
The radio activity builds on an online advertising campaign and consumer PR initiative, following the creation of a new consumer marketing team at Multimap, which was acquired by Microsoft in 2007.