On my next trip to Prague I would like to visit the Punkva caves and Macocha abyss. Can I get there by public transport or is it better to rent a car from Prague?
By public transport it's little harder to get there, but yes, it is possible:
1) Go to Brno first. The easiest and most comfortable is by bus with the company Student Agency (it's very popular transport - I recommend to buy a ticket in advance - you can do it online)
2) Brno to Blansko by train and Blansko to Punkva caves by bus
Search departures on jizdnirady.cz (there is English version)
Timetable: JMK Public Transport From: Brno To: Blansko, Skalní Mlýn
and enjoy beauties of Czech Republic! :)