Lisbon airport is located in the city and is very close to IST. You can take a taxi from the airport to IST. The taxi ride is less than 5km and takes app. 10-15 minutes.
It is also very easy and convenient to get to IST by taking the Metro Red Line directly at the airport. This will take app. 35 minutes.
At IST, look for the “Pavilhão de Civil” (Civil Engineering Pavilion).