Ibaraki (茨城県) is a prefecture to the northeast of Tokyo with the unfortunate reputation of being voted Japan’s most boring. This is rather unfair as it has loads to offer, including the plentiful supplies of fresh vegetables its fertile land provides Tokyo supermarkets with (if you get a chance try the peppery mizuna (水菜) in a salad, it’s fresh and fantastic like a Japanese roquette).
Ibaraki also houses a very famous, double-peaked mountain called Tsukuba (筑波山) which isn’t to our knowledge, swimmable (as always, investigation pending) but does afford you some of the top views of the entire Tokyo region all the way to Mount Fuji if you scale it. Apart from that the prefecture is mostly flat and collects a lot of water - with lakes, wide rivers, and a top-rated coastline for surfing and swimming.
One of the quickest beach spots to get to on a day trip from Tokyo is Hirai Beach Resort (平井海水浴場) in Kashima City (鹿嶋市).
The rather grand sounding name might conjure all sorts of images, but it’s a pretty humble stretch of (off-white, greyish) sand without a great deal of infrastructure. Surfers love it here as it gets some great pacific swell, while the swimming is also nice, with fun, ripping waves to play around in, and soft access underfoot with a gentle decline into the water.
The beach has decent facilities, with showers, toilets and taps for sandy-foot washing.
When we say humble … the Shonan coast it aint. Laying back and treading water as the waves bump you up and down your view back on land might be the large industrial area immediately south which houses at least two plants.
You’ll find the entire Pacific East coast though to be a much more laidback affair than the posh summer homes and Shonan-lifestyle of Tokyo’s southern beaches. Fewer restrictions, and arguably, more fun.