From the airport
Barajas airport has four terminals. All of theme are conveniently connected to the city by subway line 8.
Another alternative is to take a taxi, but it is more expensive and it can be a rather long trip depending on the terminal and on the traffic conditions.
The "Ciudad Universitaria" can be easily reached both by bus and by subway. The simplest possibility is to take line 6 to Ciudad Universitaria and walk north to the Faculty of Physics. This is described in this map
. Another alternative is to get off the train in Moncloa and take bus G or 82 to the stop Paraninfo-Matemáticas. Directions are provided here
Tickets are valid for both subway and bus and can be purchased at the machines and ticket counters in the subway. Prices start at €1.50 for short trips. For €12 you can buy a 10-trip ticket. Please note that you have to stamp the ticket prior to entering the subway or the bus, and that a single stamp allows you for only one trip -- unlike in other places every time you switch means of transport you have to purchase or stamp your ticket again. If you take more than five means of transport a day, you should consider buying a tourist ticket valid from one to seven days.