As a US citizen with a US passport, that will get you into most countries in Europe. A few, like Russia, require a visa, but you are unlikely to be going to those.

The general rule of thumb is, if it’s a country that it’s NOT a bad idea to go to, a passport should be fine, haha
 
For Europe, it’s really just former Soviet countries you have to worry about; Russia and Ukraine demand a visa, maybe Belarus too, I can’t remember. Other than that, you can generally travel from the Atlantic Ocean to the Black Sea on the same railpass and passport

One more note or two…  You DEFINATELY need to carry your passport when taking bus tours & trains from country to country, even if it is just a day trip.  The last two times I went to Austria & Switzerland (2003 & 2005), I took day trips from Munchen.  They never checked for a passport, because we were on a pre-paid tour bus, and I suppose they ran background checks a day or two prior for everyone on the bus, etc.  However, it could get messy for an American – if you aren’t carrying it on your person.  Also, TSA recommends you carry a passport to ALL Caribbean Isle countries, Canada, & Mexico as of 2006…  That did not used to be the case.  You could easily go back & forth to Mex, Can, Bahamas, etc. with only a non-expired D.L.

I dont quite get your post. There are several countries that require a visa that arent “bad ideas” to visit granted most of them arent in europe.
cheers
howie

 
Hehehe I was just joking I was just thinking of some of the former Soviet countries (like Russia or Ukraine) that have a crime rate comparable to America in the bootlegging era, and are potentially more dangerous than “safe” destinations in comfy old western Europe