The descent from Bernina Pass to Poschiavo is one of the most famous bike routes in Switzerland. After following this exciting route, you can take the railway back.
From Pontresina, follow the single track to the north of the pass road uphill until reaching the Montebello Curve, then follow the marked mountain biking trail via Bernina Suot to Bernina Pass. Ride along the lake until reaching the dam, then ride a bit downhill on the lane over the Priudal Vent to the Alp Grüm railway station. A bit below the station, turn off the official route and ride past Laugh da Palü lake on the rough single track to Cavaglia. From there, ride along the railway tracks until you reach a railway crossing where a bike path turns off to the left. Follow this trail, which crosses the tracks many times (caution!) and continue downhill for a long way. After riding for a stretch on a dam, you will rejoin the marked bike path. This path leads to Poschiavo, where you can take the Rhaetian railway to Bernina Pass. Ideally, you can get out there and ride along the initial route back to Pontresina.
Spundisstrasse 21, CH-7000 Chur