Take a Regional train (RE 3 or IC) heading towards STRALSUND or SCHWEDT from the new HAUPTBAHNHOF, that takes you within 18 Minutes (!) to BERNAU Bahnhof (Central station). For Euro 2, 280. Trains leave almost every hour about half past an hour.
For concrete timetable see:

 Or you take the S-Bahn in Berlin towards Bernau for example from Friedrichstrasse  (or other stations). That takes 35 Minutes for the same price.

In any case you arrive at Bernau station, leave downstairs, turn left and cross a little ugly station square, keep on the left side of a little 'park', turn left 100 meters, turn right and follow the street 300 meters till the ‚dead end’ (a crossing of another street), there you walk left, take the very  next street right, heading towards a church (Marienkirche), there you look left and see the tall Pulverturm tower and the Wolf Kahlen Museum at the foot in 200 meters distance. The Museum is only a couple of hundred meters from the station.To be on the safe side, allow yourself one hour for the entire trip to come from Berlin.
location map
from Berlin to the museum

on show now
Tibet research
Freunde der Künste Bernau
Café Leonardo von Tibet
Wolf Kahlen