Here is a map of Petřín:
Yellow cicrle is Petřín
Red circle is a Tram station from where I plan to get there (its pretty steep hill)
Orange circle is where BoN was last time, i assume it will be near the same.
Blue circle is Malovanka station (Tram, Bus)
@tomtom I would recommend to find Strahovká street and follow it, you should be able to find entrance pretty easily.
You will get to Strahovská street by getting on tram or bus and get to Malovanka station.
If its going to be like the last time, BoN takes place in two areas. One is big Arena (for 5v5, 21v21 fights) and the second is a larger place with market tents, small 1v1 arena and tents for fighters.
When you buy a ticket you will get a bracelet and you will be allowed to both places.