From the Hachiko exit of Shibuya station, turn right of the big Tsutaya and Starbucks, and walk towards Tower Records. When you get to Tower Records, turn left and walk up the hill until you get to the big intersection with Parco. Turn right here and keep walking until just before you get to a big T-intersection and a big park. You should see a staircase leading underground here on the right hand side with a sign saying Eggman.