Give me some ideas of activities to do in Romania

As of the activities that you can do in Romania, there is a plenty of selections such as:
- Swim in the Black Sea, visiting resorts like Constanta, Mamaia, Eforie Nord, Costinesti, Jupiter or Vama Veche
- You can go skiing in mountain resorts like Poiana Brasov, Azuga, Sureanu, Semenic, Cavnic, Arieseni or Ranca
- Travel the water channels of the Danube Delta and stay in traditional villages that can only be reached by boats such as Sfantu Gheorghe or Sulina
- Travel with the steam powered train Mocanita in the mountainous areas of Maramures
- Visit historical cities like Bucharest, Timisoara, Cluj-Napoca, Iasi, Brasov, Sibiu, Sighisoara
- Visit castles like Bran Castle, Peles Castle or Corvins Castle