Starting at the main station of Heidelberg the Bismarckplatz (Bismarck Square) is best arrived via the trams 5 (direction Weinheim), and 21 (Bismarckplatz), or with the buses 32 (direction Bismarckplatz, Universitaetsplatz), 33 (Richtung Köpfel) and 34 (Richtung Wilhelmsfeld).
A walk to the Bismarckplatz talks about 15 minutes.
The Universitaetsplatz (University Square) can be reached best by taking the buses 31 or 32 at the Bismarckplatz.
One gets also to the Universitaetsplatz by walking along the Hauptsstrasse (Main Street). This may take about 15 minutes.
The Max-Planck Institute for Nuclear Physics is located on the Königstuhl.
Visitors reach the Institute by taking the bus 39 to Königstuhl at the Bismarckplatz. The bus stop is called "Kernphysikalisches Institut" (Nuclear Physics Institute).
We would like to advise you that you do not try to reach the MPIK afoot. There are enough parking places which can be used.
With bus 39 you also reach (starting from Bismarckplatz) the "Königsstuhl" where the Haus der Astroomie, the Max-Planck-Institut für Astronomie and the Landessternwarte are located. You may also take the bus 30 (from Universitätsplatz) or the Mountain Railway. There are enough parking places in front of the HdA or the Landessternwarte.
A map and further information about the local transport association are given here.