A walk through the streets of old and new town is usually enough to fulfil antiquarian designs, as will a short mooch along Mokotowska. However, anybody whose anybody will tell you the real treasures are found elsewhere, namely the excellent Bazar Na Kole, an open-air market where haggling and bargaining are considered de rigeur. For full details on that check Markets. If you’re planning on taking an artwork out of the country, and it was produced prior to 1945, you will need authorisation to permit you to do so. Most shops will be able to provide you with this straight off the bat, but do check beforehand.