Road cycling races are supposed to be held around Imperial Palace Garden.
A subway, Yurakucho Line is convenient.
Get on an inbound subway at Toyosu station, “豊洲” then get off at Yurakucho station, “有楽町” or Sakuradamon station, “桜田門”. The train stops 3 stations before arriving at Yurakucho station and 4 stations before arriving at Sakuradamon station. It takes around 7 or 8 minutes and costs 170 Yen.
The Garden is to the northwest of Yurakucho station exit B2 and is to the east of Sakuradamon station exit 3.
It takes about 1 minute on foot from the stations.