Their airconditioning system is actually more of a ventilation system. In the first room we got, it was broken. Opening the window is impossible due to the Prater attractions going on until 1AM (next door is a karting, great!). We got switched to another room where the “airconditioning” worked but still it was pretty hot. The staff in the morning shift was not informed of the problem we had at night, we eventually got free breakfast to make up but the breakfast staff was not informed, and as a cherry on the cake the housekeeping just entered our room in the morning, waking us up. Would not come back here, and would definitely not recommend in summer.