Man Overboard!

On the 10th of August, 1628, the Royal Warship Vasa set out on her maiden voyage amidst pomp and circumstance. She sailed 1300 meters and sank quickly after taking on water on the port side. She remained on the ocean floor  until 1961 when a largely intact vessel was hoisted up from the deep.

If your time is limited and allows only one tourist visit, this should be it - with or without me as your guide.