Cyclists will tour the city’s bridges, tunnels, and overpasses as part of the 21st annual Tour de Somerville on Saturday, Oct. 19. This year’s tour, titled “Over, Under, Around, and Through” will also visit local construction sites as part of the 13-mile ride sponsored by the Somerville Bicycle Committee. The bicyclists will meet at 10 a.m. behind the Holland Street entrance to the Davis Square MBTA stop before departing for the tour. A rain date for the ride has been scheduled for Sunday, Oct. 20. More information is available at www.somervillebikes.org. Full story for BostonGlobe.com subscribers.