These are general descriptions from the congress hotel, The Crown Plaza, though the last parts are almost universal.
the Natural History Museum
Walk to the S-Bahn station ‘Zoologischer Garten’, enter either the S5 (to Strausberg or Hoppegarten), S75 (to Wartenberg) or the S7 (to Ahrensfelde) due East. Leave at S-Bahn station ‘Friedrichstraße‘ and take the stairs or escalators at the front of the platform than go downstairs to the U6 (to Tegel). It is easier if you enter the U-Bahn at the back of the train. Leave at the station ‘Naturkundemuseum’ via the back end exit, there should also be signs point toward the museum. There you will leave the station on the crossing Chausseestraße/Invalidenstraße, turn right into the Invalidenstraße and walk down that street until you reach no. 43. The entrance is quite recognizable due to the flags in front.
the Bunker tours
Meeting point for all three tours is outside of U Gesundbrunnen. In the image the yellow square and arrow indicate the meeting point.
Walk to the S-Bahn station ‘Zoologischer Garten’, enter either the S5 (to Strausberg or Hoppegarten), S75 (to Wartenberg) or the S7 (to Ahrensfelde) due East. Enter the train somewhere in the middle and ride to S-Bahn station ‘Alexanderplatz’. Follows the signs downstairs to the U8. On the platform enter the train heading to Wittenau (due North) at the back and ride until U-Bahn station ‘Gesundbrunnen’. Take the exit at the southern end of the platform and leave the station via the stairs. The meeting point is just on the right side of the stairs.
the public day
The public day will be very close to the Natural History Museum at the ‘Kaiserin Friedrich-Stiftung’ Robert-Koch-Platz 7. You can walk from either the Hauptbahnhof, Friedrichstraße or the U-Bahn Naturkundemuseum.