I would like to see old town Frankfurt (Roemberberg?) . We are arriving at 10 am into the Frankfurt airport. What transportation should I take to get to old town? When we want to leave for Cologne - do we go to Frankfurt am Main station from Roemberberg to take a train to Cologne? Can we store our luggage anywhere while we sight-see Frankfurt? Thanks. I am researching but a little confused.
Römerberg? From FRA airport hop on a direct train to Frankfurt Main (15m).
Yes, you can lock your bags in lockers at Frankfurt Main: https://www.seat61.com/stations/frankfurt-hauptbahnhof.htm#Luggage_lockers.
Frankfurt Main is where you'll catch a direct train to Cologne (1h 15m).
Taxi--takes about 20 minutes. Here is a link about lockers.