Not a "local" but a tourist custom... A favourite pastime of big and small kids on German beaches is building sand castles. Digging holes and canals in the wet ground just off the beach is also popular. Sand and mud invite to dig. Some people build huge ramparts around their Strandkorb and decorate them with shells or whatever they find on the beach. Here is a particularly fine sand architecture, probably done with castle-shaped moulds for "sandcake baking". Showels, moulds and everything you and your kids need to play in the sand can be obtained from each and every souvenir shop on and behind the dyke.
However, building huge sand castles around your Strandkorb, as it was popular some decades ago, is not allowed any more nowadays.
The ancient law of the sea says: finders keepers. Stranded goods belong to whoever finds them.
Modern legislation has a different approach concerning the load of stranded ships. Most likely you won’t find a whole super tanker full of petrol on the beach, though. When small items are concerned, this old law is still common usage and opinion.
The driver of your carriage told me that he has a whole collection of hats and baseball caps that he picked up on his regular rides to Neuwerk. My own best find was a watch. Quite far out in the tidelands I spotted something glittering among the mud. There was no one in sight who could have lost it, so it must have been there since at least the previous low tide. It is a pretty watch, a standard brand and not too valuable, and it kept running perfectly, and I am still wearing it almost every day.
Everywhere on the dikes you'll see sheep grazing. By keeping the grass short they are doing an important work for the protection of the coastline which no other animal could do. Sheep bite the grass off without tearing out the roots. Their little hooves do not cause holes in the turf.
A dense and solid turf cover is important. Any hole may become dangerous in case of a storm tide. The waves may hollow out the dike and cause it to break.
Dear hikers and bikers, do not walk on the grass along the dikes. Stay on the paved paths, because your shoes may very well tear holes into the turf.
The "Fischerfest" takes place one weekend in late May as soon as the season's first Matjes herring is available. They claim to have a fish buffet that's one mile long - well, I'd rather not measure. Anyway, for those who like fish, this is a great opportunity to taste fresh Matjes, all kinds of smoked fish, fish balls, grilled fish and so on and to buy canned fish specialities produced in Cuxhaven for a cheap price.
The arrival of the new Matjes in May is an event in the North. Matjes are herrings caught right after laying their eggs. The fillets are salted and then served cold either on bread with onions or with potatoes. Yum!
Where? In the halls along the fishing port (Fischereihafen), follow the crowds.