The caves are definitely worth visiting but are a bit tricky to get to. Your best bet may be to hire a driver or hire a car in Brno. If you're feeling energetic, then you can hire bikes in Brno and cycle out to the caves (there's a marked cycle path all of the way and it's a very pleasant ride). Bear in mind that the caves can book out, as there is limited capacity for the number of people that they can take in at any one time, therefore it's a good idea to reserve ahead. Also, the car park is a 25-minute walk from the cave mouth, so make sure that you arrive in plenty of time so that you don't miss your slot.