Pokémon White Version 2 Tips

Hidden Grotto Locations
Hidden Grottos are hidden all over the Unova Region. The trick to finding them is to look closely at the trees in the surrounding area. Trees that hide Hidden Grottos don't have an open patch of dirt in between them, they have a dark green spot, or some other color depending on the season, instead that makes them look like they've merged together. The Hidden Grottos are not in every location in Unova but reside in the following locations: Route 2, Route 3, Route 5, Route 6, Route 7, Route 9, Route 13, Route 18, Route 22, Route 23, Floccesy Ranch, Giant Chasm Crater Forest, Lostlorn Forest, and Pinwheel Forest. How many are in each location is hard to say, but if you enter all of them you'll get a medal for the achievement.
On a side note, you can find items, mulch, or Pokémon with hidden abilities in the Hidden Grottos every day.