Hi Meli, I have a couple of thoughts regarding your trip and hope they might be useful.  We traveled to Cornwall  in 2002 and 2004 and did it two ways.  On the first trip we took the Express Train from Heathrow to Paddington Station, mostly because I wanted to visit Paddington Station.  So much history there.  On our second trip, we took the bus from Heathrow to Reading and caught the train there, stopping in Truro for the night. Things may have changed but the car rental agency was closed on Sunday.  Also, if you'd prefer to drive an automatic car, you should probably see if they have them for rent in Penzance. I found that I could only rent one in Truro.  Here in the States we're not accustomed to driving on the "other side" so it might be a challenge to try and use a stick shift on the opposite side of the car.  Plus, we're used to traffic lights and in Cornwall the roundabout is dominant.  I've grown rather fond of roundabouts and have noticed we're getting more of them in Orange County in the less traveled areas. Penzance is absolutely lovely.  I don't know of a hotel or B & B there, we stayed closer to St Ives.  We did have dinner in Penzance, The Turk's Head.  Back then it was great!  Be sure to visit St. Michael's Mount.  It's not that far from Penzance. Catherine gave you great recommendations for getting your rail passes ahead of time.  You'll save lots of money and first class feels quite posh! Cheers, Jan Mackey