This is a mostly singletrack trail that parallels the train tracks from the train station Täsch (where there is a large carpark) to the train station in Zermatt. Zermatt is a car-free city, so this is a free alternative to the Täsch-Zermatt shuttle. If you are taking a train, it is about 20 Franks as you'll have to buy a ticket for you and the bike.
Despite paralleling the train tracks, this is not a typical rail trail. It has got some fun and challenging sections including one at about one mile into the trail where you may have to walk a short distance due to the steepness of the trail. The scenery isn't bad either!