The Isle of Man Tourist Trophy (usually called “TT”) has been run most years since 1907, since 1911 on the Snaefell Mountain Course, which consists of 60.721 km of entirely public roads, passing through the towns of Douglas and Ramsey and numerous villages along the highway. The course includes a climb and descent of Snaefell mountain, reaching a high point of 422 metres above sea level. The TT is the last remaining high-profile world-class motorcycle race run entirely on public roads.
Due to uneven road surfaces, weather conditions, and the near proximity of walls, buildings, and other hard surfaces to the road, it is considered one of the most dangerous motor sport events in the world, with 153 fatalities between 1907 and 1922 in official practices and races, or 263 if you include other race series such as the Manx Grand Prix. Fatalities among spectators (who often watch the race from the roadside) and officials are not uncommon.
Today, 2022-06-09 is the last day of Mountain Course racing in the 2022 TT, the first to be held since 2019 due to the COVID-19 hysteria.
The current lap speed record for the TT Mountain Course was set in 2018 by Peter Hickman at 16 minutes and 42.778 seconds for an average speed over the entire course of 217.989 km/hour (135.452 miles per hour) . Speeds above 320 km/hour on straights are not uncommon, with an unofficial speed record of 332 km/hour on the Sulby straight having been set during a 2006 practice lap.
Here is a bike camera view of a lap around the TT Mountain Course recorded during the 2015 TT.