O
- Olen to Gressoney
- Olimpica
- Olimpica line
- Olivine Pools
- Olivine Trail Loop
- Ollomont to Vignettes Hut
- Olperer
- Olperer 1
- Olperer 2
- Olympiabahn
- Olympia delle Tofane
- Olympiapark Loop
- Olympia to Pe Ell
- Olympic
- Olympic Discovery Trail
- Olympic Hot Springs Trail
- O'Malley Peak: Ballpark Trail
- Omalo to Girevi... the Adventure begins!
- Omas and Opas (aka The Twins)
- Ombrieux line
- Once is Enough
- Once is Enough
- One Mile Lake Loop
- One Time Only
- Onion Creek Trail
- Onion Creek Trail
- Onion Creek Trail
- Onion Portage
- Onkeljoch
- Onomea Bay Trail
- On the front line: Lagazuoi and Forcella Travenanzes
- Onza Alley
- Oolah Valley: Anaktuvuk Pass to Summit Lake
- Oolah Valley: Summit Lake to Dalton Highway
- OO Left
- Oompa Loompa Land
- Oops and Poops
- OO Right
- Opabin Prospect Out-and-Back
- Opal Hills Loop
- Opal Ridge
- Opal Ridge (Loop) | C'est Notre Monde
- Opal to Grizzly Traverse
- Open face - Past trees & turn right from top of Gron
- Oracle State Park: Big Loop
- Oracle State Park: Nature Loop Trail
- Orange Loop
- Orchard Point via Devil's Path
- Orcs
- Oregon Trail Reserve: Rim Trail Loop
- Orient Express Couloir
- Orient Rope Line
- Original Sin
- Original ski tour between Cime del Forni to Col Pale Rosse
- Ornach Ski-tour
- Orsières, Champex, Chamonix 57km
- Orsières - Moay with the Escargogo
- Ortler Ski Tour: Branca Hut to Pizzini Hut
- Ortler Ski Tour: Martello Hut to Branca Hut
- Ortler Ski Tour: Northeast Couloir of the Gran Zebru from the Pizzini Hut
- Ortler Ski Tour: Pizzo Tresero from the Branca Hut
- Ortler Ski Tour: Punta San Matteo from the Branca Hut
- Ortler Ski Tour: Sulden to Zufal Hut
- Ortler Ski Tour: Zufal to Martello Hut
- Ortveri (4365 m) NE Face
- O-Sawa
- Osberg Ridgeline Epic
- Oso Creek Trail: Out-and-Back
- Oso Creek Trail: Out-and-Back
- Oso Creek Trail: Out-and-Back
- Osorno via La Picada - North Face
- Osorno Volcano South West Face
- Ossepi Chute
- Ossmann Alm Trail
- Östliche Seespitze von Franz-Senn-Hütte
- Ostrinne
- Ostuferwanderweg
- Ostuferwanderweg am Hallstättersee
- Ost Wand
- Otero Canyon: Long Loop