The Vienna Card is a travel pass and discount voucher rolled into one. It lasts for 72 hours and gives free travel on all modes of transport within the central area. It also gives discounts on wider travel and reduced entry for a host of museums etc.
It costs only €16 but remember to get it stamped the first time you use it. Inspectors are few and far between but get caught without a ticket and you'll be fined around €65 and still have to pay for your journey. Buy it at the airport on arrival, it will save you money on the train in.
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