How did Pokemon Black 2 listen to the tide and get into Sirona's cabin? Where is it?

Ocean monument, a hidden in サザナミタンタンザナミザミザミミザザ𞢷ザザ12

Surfing: If you can go to Tingchao Town, you can definitely go.

-Machamp: I'm sure I'll get it when I get to Tingchao Town.

-Diving: displayed by NPC on the left side of Tingchao Town computer.

-Flash: It's in the second alley on the left in Feiyun.

When you get to Tingchao Bay, you can see a shadow area. Just swim over and press the A key.

There are 4 shadows on the sea surface, one in the southeast and northwest, no matter which one you enter.

Remember to press the up key all the time after entering the water, otherwise it will surface.