Summer days in Ljubljana are just ideal for enjoying the day in one of the city's outdoor cafes, exploring numerous nature paths in and around Ljubljana, taking a swim or even learning how to sup on Ljubljanica river. But if you don't like the heat at all, here are some tips.
The great indoors
You can cool off nicely among the thick walls of the Ljubljana Castle and learn about Slovenian history at a permanent exhibition of the same name. Churches, especially the famous St. Nicholas' Cathedral or the pink Franciscan Church at the Prešernov trg square are another among the cool sightseeing options in the literal sense of the word.
However, if you'd prefer to stay indoors to be safe from the heat, you should try some of Ljubljana's museums (the City Museum of Ljubljana has an especially refreshing exhibition on view) or increasingly popular Escape Rooms.