In a week I'll be travelling from Sofia to Copenhagen, but with a transit through Vienna. I'll be arriving at 9:00 and my next flight is at 15:15, which makes a total of 6h15m. I thought this could be enough to grab a quick peak at the city and maybe one or two of the tourist attractions, since I've never been to Vienna before, but I heard it's certainly a place worth visiting.
Are these 6 hours enough to go in the city and check out at least one or two of the most popular tourist attractions, and which of them are closest to the airport?
(I'm an EU citizen, and I'll be travelling with no luggage, so hopefully I won't have to spend too much time at the airport dealing with luggage/passport control).