Sopot originates in 7th century as a Pomeranian stronghold. Initially it was a commercial trade outpost for commerce extending both up the Vistula river and to cities north across the Baltic Sea. Place worth to see - depending on personal preferences - in July and August too crowded. Weather is still nice May-June/September-October.
In Sopot, if you go little off the main streets, you can see beautiful old housings and villas.
In Sopot there is long and beautiful woodden bridge 515 m long, that goes into the sea - this is how it looks under.