First, in the tunnel, it looks like the bedrock is exposed--there's a station on MARTA in Atlanta like that. But when you give the stone a tap, it reveals it's fiberglass facing.
When you pass through the turnstile and turn left, you see this:
It is apparently a tribute to the Korean movie awards, because around the corner, the whole hallway is covered in awards show stills:
Finally, the entry plaza walls are covered in decorative tile murals. And check out those crazy phone kiosks.