Warsaw has two airports operating international flights:
- Chopin: main airport, major airlines, located within the city
- Modlin: cheap airline airport, only RyanAir flights from all over the Europe, located 35km from Warsaw
Warsaw can be reached by direct trains from Berlin, Amsterdam, Prague and Vienna.
Polish Railways schedule is available here: PKP. The main station is called Warszawa Centralna.
Astronomical Observatory of the University of Warsaw (in Polish: Obserwatorium Astronomiczne Uniwersytetu Warszawskiego listen)
Aleje Ujazdowskie 4 00-478 Warszawa
For public transport itineraries check warszawa.jakdojade.pl. Example route to the Workshop venue from the Chopin Airport:  The nearest bus stop to the Observatory is called Plac na Rozdrozu (pronunciation). From Chopin Airport there is a direct bus no 188, reaching Plac na Rozdrozu in 40 mins. From there it is a 5 minute work South to the Observatory.
From Modlin Airport the best option is to use Modlin Bus to reach Warsaw City Centre. From there you can either use trams (4, 18, 35) to Plac Unii Lubelskiej  or Metro M1 line, one stop to Politechnika, and then walk for about 10 mins.