Tallinn's Hotel Viru was built in the early 70's and was a secret home to the KGB during the Soviet era. 

It was mandatory that any visitors to the city stop over in the hotel so that the KGB could keep tabs on movements in and out of Tallinn. 

The KGB took over an entire floor of the building, using it as a radio centre and a hub to spy on hotel guests. 

Espionage devices were discovered following Estonian Independence in over 60 of the hotel rooms.