Need advice on Frankfurt 9-hour layover (12AM-8PM). Enough time to go into town? How are the security lines in the late afternoon for international departures? (My transfers have always been in the morning)

Generally it is only the US security line that is a problem at FRA, and in the afternoon it is much shorter than in the morning. Almost bearable. After 8 pm there are a cluster of non-US departures but with normal lines.

As for leaving the airport, the S-bahn is 30 minutes to Mainz, which is a nice small town on the Rhine. Good for a walk, some shopping and a beer.

You don't say what date or day (of the week) you have the layover, but Sundays can be kind of slim pickings.
The closer it gets to Christmas, the more stuff there is to see and do (ChristkindleMarkts!)
The Zeil is a nice shopping area if you are so inclined.

As for the S-bahn/U-bahn tickets, probably the easiest thing to do is just to get a day pass. You can buy one either at a ticket machine or at a counter at the train station, which is connected to the lower ground fl of F'furt airport. Just follow the sign for trains or S-bahn. That way you get free rides without worrying about whether you have the correct fare or not

Mainz is nice and I am also kind of partial to Heidelburg-- has a charming old town and very scenic, right on the Nekkar River with a castle on the hill that you can tour. Weisbaden would be nice if you wanted to sit in the hot springs.....after a long flight.....I do this on my layover to Africa.

again, date would be important to know, because sundays roll up pretty tight in Deutschland!

Just repeating my standard Bad Homburg spas recommendation. Should be around 45 minutes from FRA by S-Bahn ( local train ) & a short taxi ride from Bad Homburg station. The addresses and homepages can be found with the FT search function.

Just use the search function in this forum and in the M&M forum I can remember at least 4 threads in the past month where we discussed this issue.

mosburger, maggie6872 and number_6 still posted some interesting information and you'll find a lot more in the other threads. And as maggie6872 pointed out it would be also important to know the day (weekday and month) you are in FRA. For example mosburger's advice makes much more sense on weekdays at the spa in BAd Homburg is quite crowded on weekends IIRC.

Anyway there a lot of things to do and there is no need just to hang around at the airport doing nothing� Enjoy your layover.

Cheers
totti

I think Heidelburg is a little far for a nine hour layover. Mainz is easy, although now you mention it, many shops did seem to be closed on Sunday. I don't shop, so it didn't interfere with my activities. Sunday is the free day at the Natural History Museum in Mainz. Here is my diary entry for a Sunday in Mainz in January if it helps anyone:

http://peachfront.diaryland.com/germjan06p3.html