Must-see for K-pop (especially SM) fans, but other than that, there's nothing to do here except hope that you may meet idols.
It's easy to get there, if you get lost, just keep walking ahead of FNC Entertainment Building. You'll find a park, walk to your right and voila SM building. Good luck and take a pic if you are a fan =)
be very patient if you want to spot someone famous, but its a nice place to at least take a pic and make friends with other fans