Actually coming back it IS possible to do Vienna to Brussels in one day, 650am train to Frankfurt, 1355, then 3-hour trip to Brussels arrive 6pm, could spend Friday night in Brussels. But what for? Empire crap. 5th crap. Prefer Gare du Nord early. Better to check out Frankfurt strip clubs on a Friday night surely?! Yes. Christ, it is EXPENSIVE though. Brussels to Frankfurt, Frankfurt hotel, Frankfurt to Vienna (82), Vienna hotel x 3, Vienna to Frankfurt (82), Frankfurt Hotel FRIDAY night, Frankfurt to Brussels. OH BUT TO SEE VIENNA AT XMAS!!!!! THREE nights in Vienna in December! Yes do it. Book hotels in October. Will then have November and December paychecks to pay off the credit cards/DB tickets/hotels.