The institute is located on the 10-th floor of the high-rise building in the MFF UK campus near a bridge over Vltava river (see the photo above).
From the station "Nadrazi Holesovice" of the underground line C (the red one) use the stairway on the south end of the platform and take the bus number 201 or 112 (the "ZOO bus"). Get off the bus on the first stop (right after crossing the Vltava river). These bus stops are on demand, so you will need to push the stop button when the bus is crossing the river. The names of the stops are "Kuchynka" (on line 201) or "Pelc Tyrolka" (on line 112).
If you don't want to wait for the bus, the walk is about 15 minutes from the north exit of the "Nadrazi Holesovice" station of the underground line C depending whether you choose the old or the new bridge over the river. (The latter takes about 17 minutes, but it is nice walk over and along the river.)