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, 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)
Address: Aleje Ujazdowskie 4 00-478 Warszawa
The Observatory is located together with the Botanic Garden (the same entrance from the street).
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 walk South to the Observatory (will be located on the left).
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.
Here is the list of hotels in the city centre and closer to the Observatory:
- Hampton by Hilton
- Novotel Warszawa Centrum
- MDM City Centre
- Castle Inn
- Ibis Stare Miasto
- Belwederski the nearest to the Observatory
An alternative is AirBnB, where you can find a small flat for less than 50 euro per night 
Some budget options: