The Yodogawa River flows from the confluence of three rivers in Kyoto Prefecture, down through Osaka, before emptying into the sea at Osaka Bay. This is one of a series of 300 caches hidden along the riverside. The numbers are completely random. "Usual types of containers" include magnetic bottle tops, Frisk and Mintia containers, home-made envelopes, etc. "Usual places" may be white crash barriers, guardrails, inside gate lock boxes, or on bridge structures.