Interrailer train tickets in Europe (for EU residents) allow the ticket holders to travel on regular (non-high speed services) across Europe for a fixed price and a given time.
Prices are discounted for young adults (under 28 years old) making this ideal for first trips to popular destination!
From the heatmap they are hot destination with benefits for youths that are unaccompanied by adults! Budapest, Vienna, Prague, Amsterdam and Berlin...