Has anybody gone here from Rome? Thought it might be an easy train ride and perhaps a good place to hike? Other recommendations are welcomed.

Here's the info I ran across on it:

In wine country 25km from Rome and situated on the rim of an extinct volcanic crater which contains a beautiful lake. Surrounded by a protected green area. The town of Castelgandolfo is 426 mtrs. above sea level, and is a papal summer residence.

hansikday, I was there last week, although I was on a motor coarch tour, and continued on to a couple of other small towns and ended around sunset in Frascati. It was very green and lush around Castel Gandolfo, and the lake is beautiful.

BC

Yes went by train, frequent service from Rome Termini; commuter train taking about an hour. Neat old town and lake nearby. On the same train line is Frascati, another nice old town. Hike from one train station to another; stations just a few miles apart.

I have just posted my reply here but I have no idea where it went....Ok I try to post if again.
I lived in Genzano, which is near Castel Gandolfo and IMO Castel Gandolfo is not worth a day trip, I mean there are many other interesting trips you can take from Rome, like going to Tivoli and visit Villa Adriana and Villa D'este or see Ostia Antica. Castel Gandolfo has the summer papal residence but now the Pope is in Rome and anyway you can't visit the residence. It takes about 1 hour to walk leisurely around the centre and the only other alternative is to hike down the lake (about 20 minutes on foot), but nothing really impressive. Anyhow, you can take a train from Termini Station directed to Albano Laziale and get off in Castel Gandolfo, and from there either walk up to the town or down to the lake, as the station is on the hill side. That's almost all you can do there. You need to waaaaaalk to reach Frascati from Castel Gandolfo on foot, better to take a Cotral bus that takes you there. IMO Tivoli and its 2 Villas are more worth a visit or also to Ostia Antica for its archaeological remains.

And couldn't you get to Ovieto in about the same amount of time?

Just a quick comparison: if you take the train from Roma Termini to Castel Gandolfo the trip takes about 50 minutes (and it is about 20 kilometres from Rome! I know, but it stops several times and it goes slowly...).
Rome-Florence is 316 kilometres and if you take the Eurostar you can be in Florence in 1 1/2 hrs, have a wonderful day in Florence and then come back in another 1 1/2 hrs by train. I did it with my fiance last november 2002 (taking the eurostar early in the morning, arriving at Firenze Santa maria Novella at about 9.30 am and enjoy the whole day there and then at about 6.00pm take the train to Rome... Great day...