Montblanc is easily the Holy Grail for luxury writing equipment. Don't believe me when I say my vision isn't clouded by the effervescent Eva Green as their spokesmodel.
Pens range from ballpoint to fountain, some with diamonds cut a la etoile(star-shaped) at the top of the pen(in the thousands), some without(in the hundreds). I think it's fair to say that once you go with Montblanc, it's pretty hard to go back.
Though, refills are hard to track, this location is great for authentic ones. They will also engrave your Montblanc at this location. Aside from the Yorkville hours, this is a great shop to buy gifts and they house everything from Perfume to Jewellery as well.