When you arrive at the airport, just take a taxi to the Radisson Hotel (address: Cuspide 53, Colonia Parques del Pedregal, 14020 Mexico City, Mexico). There are a number of airport taxi companies, all on a prepaid basis. Give them the hotel name and they will tell you the price which should be between 300 and 400 Pesos (MXN). The exchange rate is roughly 19.50 MXN / USD and 22 MXN / EUR. You can usually pay by cash or card, where in the former case you may want to double check your change. You are not required to give any tip, but you can give a small tip like a buck.
We are trying to set up a shuttle service between the hotel and the Physics Institute, but the first day (Monday, March 18) is a holiday and you better take a cab or Uber (which works well in Mexico) or arrange with one of the locals to be picked up.
Circuito de la Investigación Científica s/n, Ciudad Universitaria, Coyoacan;
the Theory Department is on the second floor of the main building (Edificio Marcos Moshinsky)
If you will be reimbursed for your flight, it will be in cash in MXN (the best rate to change it to USD is at the airport in Terminal 1). If not, and you like to have some cash on you, Jens will be more than happy to exchange your Euros to Pesos at mid-market rates.
There are two malls in the vicinity of the hotel: The very large shopping center Perisur across the city highway Periferico has many restaurants and a food court; the smaller mall Cuicuilco across Insurgentes Sur has further restaurants and a highly recommendable brew pub.