If you want really good adventure, you can come to Serbia. There is a plenty of things you can do especially in Kolubara Disctrict. For example Vrujci spa has aqua park with healing water https://www.banjavrujci.info/english/about-banja-vrujci/healing-properties/ and you can do paraglyding on a near by mountain Rajac. You can go to Divcibare for skiing and other winter sports. This mountain is well known for good air. Also, domestic food, nice girls and a lot of new hotels and apartmnts. Also you can check here all the other things you can visit (and there are plenty) https://www.divcibare.org.rs/en/divcibare/surrounding-area/ . I guarantee that not only you wont regret but you will surely come back again. A lot of historic heritage, mountains, rivers... Hiking trails and a lot more you can see on provided links. Have a great trip and welcome to Serbia!