personal highlights

1. UNO City: high security area with ugly buildings for 5'000 people
2. Donauinsel: sophisticated flood protection system stretching for 21 km
3. Donaupark: beautiful park, but utterly abandaned and empty in autumn
4. DC Towers: with 220m Austrias highest building (expensive elevator)
5. U-Bahn: crossing the wide Danube river on a bridge 

image sources

1. Donauturm (TV tower) @ Donaupark
2. View on Danube @ DC Towers outlook
3. View on UNO city @ DC Towers outlook
4. Lake with tree and grass @ Donaupark
5. DC Towers facade @ ground level