There are beautiful bike lanes on Lidingö. If you are coming from Stockholm, you bike over the Lilla Lidingö bridge. When you have crossed the bridge, turn left and follow the bike lane (road work without car traffic for the first 500 m) along Norra Kungsvägen until you reach the large roundabout where you have Lidingövallen on the right with TCS Lidingöloppsmässan/number bib distribution and on the left Grönsta Gärde with all finishes and some starts.
You will find the bike parking next to Grönsta Gärde.