My friend and neighbor on Harbour, Lalo Telling, wrote about the great Second Life Railroad on his fantastic blog the other day. Please do follow the link and read all about the SLRR. Going for a ride is a most enjoyable way to see the mainland and find things you never would have seen otherwise. I absolutely loved slowly meandering through sim after sim, lazily watching the landscape pass by. Some of the builds you will see are 5 and 6 years old, making this experience a trip through virtual history.
You really do owe it to yourself to read Lalo's blog and add him to your blog reader. He has been writing about the history and the current state of some of SL's oldest mainland. His blog generally is a fantastic read and a must for all you explorers!