Glass Beach in Port Allen, on Kauaʻi's south shore, is an unusual beach where decades of dumped industrial waste has been transformed by the ocean into something beautiful. The town used this stretch of shoreline as a dump from roughly 1900 to 1980, and the surf has spent the decades since grinding bottles, crockery, and pottery into smooth, rounded pieces of sea glass that wash up in every colour — green, amber, white, blue, and occasionally red or purple.
The beach is not large, and the quantity of glass varies with the season and recent weather. After heavy winter swells, the glass concentrations are highest. It is a quiet spot, mostly visited by locals and curious travellers who have heard about it. Swimming is possible but the shore is rocky and there are better beaches nearby; most people come to walk and collect.
Taking glass from the beach is technically against county rules and in practice reduces what future visitors will find. Worth keeping in mind.