Galleria Department store is one of the best. There are 2 branches in Seoul. The branch in Apkujong-dong has 2 buildings.

Apkujong Branch
Location: Apkujong-dong
Transportation: Subway (Line 3) orange line to Apkujong station and then hop in a taxi and ask for the Galleria
Telephone number: 02-3449-4114

Chamshil Branch
Location: Chamshil-dong
Transportation: Subway (Line 2) green line to Chamshil station then walk about 2 minutes
Telephone number: 02-410-7114