These places are called Hidden Hollows. These are places where you can get DW ability Pokemon ingame. Meaning that Miccino you fainted has Skill Link. There are many places like these.
Look here under Hidden Hollows to see the areas and Pokemon inside them.
Oh yeah, sometimes there can be items instead of Pokemon. You may need the Dowsing Machine.
I'll put the list here for reference.
Route 2
- Nidoran M/F (Hustle), Granbull (Rattled), Watchog (Analytic)
Route 3
- Lombre (Own Tempo), Manectric (Minus), Bibarel (Moody), Pachirisu (Volt Absorb), Zebstrika (Sap Sipper)
Route 5
- Liepard (Prankster), Mincinno (Skill Link), Foongus (Regenerator)
Route 6
- Woobat (Simple), Foongus (Regenerator)
Route 7
- Watchog (Analytic), Cubchoo (Rattled), Zangoose (Toxic Boost), Seviper (Infiltrator)
Route 9
- Muk (Poison Touch), Liepard (Prankster), Garbodor (Aftermath), Bouffalant (Soundproof)
Route 13
- Tangela (Regenerator), Spheal (Oblivious), Drifloon (Flare Boost), Skorupi (Keen Eye), Foongus (Regenerator)
Route 18
- Fearow (Sniper), Kingler (Sheer Force), Dragonite (Multiscale), Chatot (Big Pecks)
Route 22
- Pelliper (Rain Dish), Amoonguss (Regenerator), Mienfoo (Reckless)
Route 23
- Golduck (Swift Swim), Gligar (Immunity), Zangoose (Toxic Boost), Seviper (Infiltrator), Absol (Justified)
Sangi Ranch
- Marill (Sap Sipper), Dunsparce (Rattled), Herdier (Scrappy)
Pinwheel Forest
- Butterfree (Tinted Lens, White 2), Beedrill (Sniper, Black 2), Poliwhirl (Swift Swim), Murkrow (Prankster), Breloom (Technician), Hariyama (Sheer Force), Medicham (Telepathy), Bagon (Sheer Force), Amoonguss (Regenerator)
Lostlorn Forest
- Pinsir (Moxie), Heracross (Moxie), Combee (Hustle), Leavanny (Overcoat)
Giant Chasm
- Clefairy (Friend Guard), Ditto (Imposter), Sneasel (Pickpocket), Metang (Light Metal)
Abundant Shrine
- Vulpix (Drought), Golduck (Swift Swim), Swablu (Cloud Nine), Bronzor (Heavy Metal), Amoonguss (Regenerator)
