I am travelling with 2 friends to Europe in May and am looking for
alternatives to flying from Warsaw Poland to Sofia Bulgaria.  Can we
take a train?  Approx how long would it take and how much would it
cost?
Do Americans need a special visa for Bulgaria or can we get the usual
90 days upon arrival as is the case in Poland?

Dear Genki,

You could take a train, but I am not sure I recommend it. 

There's a daily train from Warszawa Centralna to Sofia through
Budapest (where you'll have to chage trains) every day. It starts on
07:30 in Warsaw, and arrives to its destination 37.5 hours later. I've
been told that this costs about EUR 182, but this might be cheaper in
Warsaw, and in any case, there are always special student/seniors
discounts - the best thing to do is ask in the train station. In any
case, with 37.5 hours of ride, think also about the advantage of
paying extra for sleeping cabins.

Another train that leaves Warszawa Centralna each day, and goes
through Vienna and Belgrad (you'll have to change trains in both
countries). It takes "only" 35.50 hours. Here, I've been told that it
will cost EUR 140.

As for "ENTRY REQUIREMENTS: A passport is required. U.S. citizen
visitors who enter the country on regular passports without a
Bulgarian visa are authorized to stay for a total of 30 days within a
six-month period." (SOURCE: U.S. Department of State, Bureau of
Consular Affairs, Washington, DC 20520, "Bulgaria"
<http://travel.state.gov/bulgaria.html>).

However, you must also remember, that if you choose the second path,
you go through Serbia and Montenegro: "ENTRY REQUIREMENTS: U.S.
citizens require a passport and visa. The Department of State strongly
advises American citizens not to attempt to enter Serbia or Montenegro
without a valid visa or tourist border pass. While border passes in
lieu of visas have been available at border crossings in the past,
this procedure is currently under review and may be discontinued or
changed without notice. Persons intending to enter Serbia and
Montenegro on the border pass system should consult the Serbia and
Montenegro Embassy or Consulate General to verify that the border pass
procedure will be available at the time they intend to visit."
(SOURCE: U.S. Department of State, Bureau of Consular Affairs,
Washington, DC 20520, "SERBIA AND MONTENEGRO"
<http://travel.state.gov/serbia_montenegro.html>). Entry requirements
for Austria are similar to those to Poland (up to 90 days without
visa).

Now, why am I not recommending a train ride? This is not a researched
opinion, but based on my experience. It seemed to me, that Westerns
are sometimes being hassled on borders in Bulgaria (perhaps in an
attempt to receive bribe); in Hungary and certainly if you go through
Vienna, people from Bulgaria and Romania are being triple checked for
every certificate on the borders between Bulgaria and Hungary. In any
case, the border police in Bulgaria is extremely inefficient, and it
will take much more than 37.5 (or 35.5) hours to go through this
journey.

This is winter, and there are probably some cheap flights from Warsaw
to Bulgaria's Black Sea resorts (and maybe also to the "Bulgarian
Alpes"). Try to see if you could get a charter deal from Warsaw to
Bulgaria that way. Good luck and have fun in that beautiful country,
with one of the best cuisines in Europe...

I hope that answered your question. I was aided with the following sites: 
Polish Railway Company: http://www.pkp.pl/en/indexen.html 
German Railway Company, hotline : http://www.bahn.de/pv/view/index.shtml 
State Department: http://travel.state.gov/ 

Please contact me if you need any further clarification on this answer
before you tip/rate it.