HOTEL ZURIQUE (***) makes a special price for the ICMI 25 conference (65€ / night). To get this price, it is necessary to use the code “ICMI Study 25” and book via e-mail to res.zurique@viphotels.com
This hotel is not far from the University. You may walk (about 20 minutes) or use the underground (2 stations, from Campo Pequeno to Cidade Universitária). From Hotel Zurique you may go easily to the center of Lisbon using the underground (from Campo Pequeno, in the opposite direction).
https://www.viphotels.com/en/Hotels/VIP-Executive-Zurique/About-Hotel.aspx
To make the reservation and to sort out questions with the hotel the e-mail is: res.zurique@viphotels.com
If you want a better or a cheaper accommodation there are many options that you can look at in Booking or Trivago or doing a Google search