Hietalahdentori is a very large square at the west end of Bulevardi so basically continue west along Esplanadi to the south of the Swedish Theatre and on almost to the dock. A very large flea market is held here, I think daily. You would have to be up very early to beat a dealer to a rare early piece of mid-century design but there were good spreads of Iittala so this might be the place to look for a replacement piece for the one you broke years ago to make up the full set and there were quite a few Marimekko dresses and bags if you are looking for second-hand bargains.
Across the north side of the square is the market hall built in 1903. At the moment this has food stalls with amazing spreads of vegetables, fresh meat and of course fish with bakery and coffee stalls. I believe that these have been moved here temporarily - displacing books and antiques - while the building of another food market is being restored.