The main entrance to the Mathematics building is currently closed. If you are standing in front of the building you can either take the stairs behind you back downstairs and enter the building on the ground floor or take the (few) steps on your right, turn left and enter the building through Physics. 

If you need more detailled directions, then please use the link Campus Navigation and enter H16 as destination. The app is expected to know about all access restrictions due to ongoing construction work.