In the sea

Walk out a long the sea wall, she waded down the steps and into the cool water. It was beautiful but still a bit cold. She had hoped no one had seen or followed her. All this time researching and planning, she had finally made her way here to retrieve what no one else could find. And she only had a little bit of time while the tide was low. She dunked herself under feeling along the rocks for the exact spot then pushed on the rock. It moved opening a secret door to an underwater room. She dunked herself under again just to be sure studying the room. She pushed the rock again and the door closed as she surfaced. She surfaced and smiled mischievously. She wasn't exactly dressed for this, but she'd found the secret room. She'd be back later, better prepared to investigate further.

Thanks to @Alter_Ego for bits of the prompt to arrive at this creation.