Mikata Goko

Five lakes sit side by side behind the dunes of Wakasa Bay, connected to each other and to the sea by narrow channels, and each one holds water of a different salinity. Mikata is fresh, Suigetsu and Suga are brackish, Kugushi is saltier, Hiruga is nearly seawater. The different chemistry gives them visibly different colours, which is why they are marketed as the five-coloured lakes, and it is not entirely a marketing line.

The interesting one is Suigetsu. It is deep, has no inflowing river to stir it, and its bottom water holds no oxygen, so nothing burrows into the sediment. The result is 45 metres of undisturbed annual layers, one per year for about 70,000 years, alternating dark clay and pale algae. Cores drilled here are now the international reference used to calibrate radiocarbon dating worldwide. The Varve Museum in Wakasa town displays a 45-metre run of the core along a glass wall, which is the longest continuous piece of time you can look at anywhere.

Above the lakes, the Rainbow Line toll road climbs Mount Baijo to a set of terraces with a chairlift and a cable car, and from the top all five lakes and the bay are visible at once. Go on a clear day; in haze it is just water.

Around the shore: kayaking, plum orchards that supply Fukui's pickled plums, and grilled freshwater eel that the area has been known for since the Edo period. A car is the only practical way to do it. The nearest station is Mihama on the JR Obama line.