The faculty department building at Troja is filled with red. The path from the nearest subway station "Nadrazi Holesovice" (line C) to the faculty is marked in the map by the dotted red line (about 12 min). To walk, use the exit in the front of the train with which you arrived.
When traveling from the central Prague, the faculty department building at Troja is a high, twelve-floor glass building on the right-hand side just behind the bridge "Most Barikadniku" across the Vltava river. The entrance is located in the low building right to the department building (behind it when viewed from the bus station "Kuchynka"). The Department of Geophysics is located on the uppermost, 12th floor.
Note that a better quality GIF version of the above map (150 kB!) is also available.