Kiwiline, there is an old problem with such connections when booking anything else than seats (e.g. sleepers or couchettes). The case is that OeBB website in Austria-Poland routes sells tickets only for seating carriages, while in case of Vienna-Krakow overnight connection there are actually just two carriages (one sleeper and one couchette) attached to Vienna-Warsaw #406 train, thus OeBB website can't sell you anything for 10pm departure. Solutions for you might be as follows:
a) simply contact OeBB directly via
contact form and order you tickets using other booking channel. OeBB can either mail it to you by regular mail (extra +5 euro) or you can pick up ticket once already in Austria. Also possible to contact OeBB
by phoneb) go with daytime trains. There are no direct ones to Krakow during the day, but a few connections go via nearby Katowice (tickets, including discounted, can be bought online for connection Vienna-Krakow, thus you will need just make an easy change and nothing else)
p.s. also bringing your attention that according to
OeBB with Austria-Poland connections "
Children up to their 15th birthday travel free of charge, if they are accompanied by their parents/grandparents"
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