Tunnelling Through the Alps in Switzerland
The Gotthard Base Tunnel (not to be confused with the older St Gotthard Tunnel) is being built between Erstfeld and Bodio. It's going to be quite something:
- 57 kilometers (about 36 miles) long
- 2 kilometers (about 6600 feet) underground
- geothermally heated to 50°C (122°F)
- 300 trains will pass through its two tubes daily
- ¼ the cost of the shorter Chunnel
- should be completed by 2009
This New Scientist article has some interesting details on the engineering and construction challenges, and the risks of such a tunnel.
Looking for more? Here's a piece on the history of the Gotthard railroad, which includes an excellent illustration showing the magnitude of this endeavor. This page has some engineering details. This PDF has some more. And here's some more information on safety.