Unfortunately, the Rohrbacher Street, the connection from the Heidelberg main bus hub "Bismarckplatz" to "Alois-Link-Platz" will be blocked due to construction work (one way only).
Buses to MPI Kernphysik therefore will leave from Heidelberg main station (Steig L)
Note: You don't have to panic if you see the bus across the street on Steig P as it stops there on the way back (but passengers are not supposed to board there).
Bus No. 39 (direction Königstuhl) leaves on every full hour (:02) and brings you directly to our institute in 13 min.
Bus No. 39A (direction EMBL/Mombertplatz) leaves irregularly (but mainly :25), you'll need to exit at Bierhelderhof/ Ehrenfriedhof and walk uphill (200m) to our institute
From MPI Kernphysik (39) the buses go directly from Alois-Link-Platz to the main station, from Bierhelderhof (39A) almost all buses will go via Bismarckplatz.
Best option is to buy a 9 € ticket for the month of July (online or at any ticket machine) valid for all (regional) trains and buses in Germany.
https://www.rnv-online.de/english/
Please note that Deutsche Bah (DB) might still give you a wrong schedule,
please use: https://www.vrn.de/