BY PUBLIC TRANSPORT
There are two alternatives:
The usual way would be taking a metro line C (from the train station or bus station and elsewhere) to final station Haje and then a bus 387/381 straight to the castle,which you can also use for returning on Friday, please see the timetables in the attachments.
If you arrive to the main train station (Hlavni nadrazi), you can take a train to S9 (direction Benesov u Prahy) to station Říčany and switch there to a bus 387 to the station Kostelec (Kostelec n.Č.l.,Nám.), please see the route and timetables here - https://goo.gl/maps/pDG9dmU4D4m.
IMPORTANT NOTE WHEN ARRIVING ON MONDAY
The Prague City department decided to do a subway reconstruction specifically and only on the day of the arrival to the conference, Monday 22nd.
You can use the substitute transfer bus for metro, and take the red line metro C to the final station Haje, but you would have to switch for an X bus for a couple of stations in between. It sounds complicated but there is a good system of navigation.
General information about Prague:
Journey planner: http://spojeni.dpp.cz/ConnForm.aspx?tt=PID&cl=E5
Transportation info (fares): http://www.dpp.cz/en/fares-in-prague/
If you decided to arrive by car, please look at this route - https://goo.gl/maps/ERiuJNXC1L42
Alternatively, if you would let us know the approximate times when would you like to arrive and depart, we would be happy to try arranging a ride for you, for example with some of the invited speakers or someone from our lab.