There are guided tours which must be booked in advance. They start every hour from 6 pm till 11 pm and on the weekend from 11 am to 11 pm.
More information http://themoscowcity.com/en/building/delovoy-kompleks-imperiya#.Wpps3ujOU2w
Coordinates 55°44'53.37" N 37°32'24.801" E