“I've got gadgets and gizmos a-plenty. I've got whosits and whatsits galore.”
―Ariel singing about her treasures
Ariel's Secret Grotto is a special place where Ariel keeps her vast treasure trove of human objects, antiques, artifacts, and other stuff that she has collected. Each one has a special place in her heart.
It is a large cavern that has a large round stone covering the entrance. Inside are hollowed out shelves for which she stores and displays her discoveries.
After finding unusual objects throughout exploring places like shipwrecks, caves, and even sometimes above the surface, she puts them in a small pink shoulder bag and takes them back to store in her grotto. The Dinglehopper (a fork) is one of them.
Ariel has collected many things, each representing a special memory, adventure, or new discovery. She calls them her gadgets, gizmos, whosits, whatsits, and thingamabobs.
She had two collections stored there: The first one was started by her, after she learned to not be terrified of humans in the TV series. She was forced to destroy it after Ursula cursed it to attack Atlantica.
The second one was started at some point between the TV series and the film. It ended up being accidentally discovered by Sebastian who was keeping a watch on her at the time (and presumably started up again without his knowledge, based on his reaction to it) and then destroyed by King Triton when he was angry with Ariel upon learning that she rescued and fell in love with a human, especially when he saw she had a statue of him there as well. However, he becomes horrified and regrets his actions, leaving a weeping Ariel alone in her ruined grotto in shame. He later returns to find her only to discover she disappeared and orders a search for her to apologize for what he had done.
Its reappearance in the sequel implies that either Triton magically rebuilt it as a sign of atonement for his past violent outbursts or that not all of it was destroyed. While the former is mostly likely, the latter at least must also be true, for one of Ariel's found paintings, Georges de la Tour's Penitent Magdalen and the Smoking Flame, is currently in a Los Angeles art gallery.
Her collection has included:
A smoking pipe
A grandfather clock
Jack in the Box
Entrance to the grotto
The hole in the top that allows light to enter
Ariel admiring her collection
Ariel exploring the painting "The Penitent Magdalen with the Smoking Flame" by Georges de la Tour
Prince Eric's statue added to the grotto by Flounder