However, there are a few places in Black and White 2 that might be what you're looking for:
* Dreamyard: This area, accessible via the C-Gear and the Dream World, features a changing environment with a variety of Pokemon to encounter. You can access it multiple times a day with different Pokemon appearing each time.
* Abundant Shrine: Located in the Undella Bay area, this shrine changes its Pokemon depending on the time of day and the current season. It's a good spot to catch rare Pokemon.
* The Lostlorn Forest: This dense forest is home to a variety of Pokemon and can be explored with a Poke Radar. It's a great place to find rare and powerful Pokemon.
Perhaps you were thinking of Hidden Grottos from other games like:
* Pokemon X and Y: These locations were accessed through the "Secret Super Training" feature, providing training opportunities for your Pokemon.
* Pokemon Omega Ruby and Alpha Sapphire: These locations were accessed via the "Super Training" feature, offering a different training experience for your Pokemon.
If you could clarify which aspect of "Hidden Grottos" you were thinking of, I could give you a more specific answer.