Complex sentence: The Gotthard Base Tunnel (GBT; or "Sankt-Gotthard-Tunnel";;;) is a railway base tunnel through the Alps in Switzerland, which opened on 1 June 2016 with full service to begin in December 2016.
Split into simpler sentences: The Gotthard Base Tunnel (GBT; or "Sankt-Gotthard-Tunnel";;;) is a railway base tunnel through the Alps in Switzerland. It opened on 1 June 2016 with full service to begin in December 2016.