What happens on a fair, sunny day or on a hot day?

The Danube tends to warm up not more than 25 defrees Celsius (77 degrees Fahrenheit), so cruising on a boat is a refreshing activity on a hot sunny day.  The boat has two decks. Passengers on the upper deck are protected by a sun shading cover. If you already had too much of the sunshine, then you go down to the lower deck at any time and enjoy cruising in an air-conditioned environment.