There are connections from London to Inverness and Fort William (including overnight sleeper service), as well as reliable links from Glasgow and Edinburgh. For information call First Scotrail.
Though there is no rail connection among towns within the Great Glen, this area has the West Highland line, which links Fort William to Mallaig; a trip on this scenic line is recommended (steam trains are a bonus in the summer months). There's train service between Glasgow (Queen Street) and Inverness, via Aviemore, which gives access to the heart of Speyside.
First Scotrail (08457/484950. www.firstgroup.com/scotrail).