Colin Monteath / Trekker at dawn, Kaikoura Walkway, Seaward Kaikoura Mountains behind, New Zealand

Colin Monteath / Trekker at dawn, Kaikoura Walkway, Seaward Kaikoura Mountains behind, New Zealand

David Noton / Woman on canopy trail through tropical rainforest nr Arenal, Zona Norte, Costa Rica

Philippe Clement / Tourists looking over cloud forest at Monteverde NP, Costa Rica

Mark Raycroft / Black Labrador Retriever (Canis familiaris) adult reclining on walkway

Mark Raycroft / Miniature Schnauzer (Canis familiaris) sitting on garden walkway

Steven David Miller / Looking down from skyrail on the rainforest canopy of Barron Gorge NP, Queensland, Australia.

Steven David Miller / Looking down from skyrail on the rainforest canopy of Barron Gorge National Park, Queensland, Australia

Nick Garbutt / Birdwatching from canopy walkway, Danum Valley, Sabah, Borneo, 2006

Pete Oxford / People on canopy walkway, ecotourism in Amazonian Rainforest, Ecuador

LYNN M. STONE / Oeschinensee lake, Alps, Switzerland

Doug Wechsler / Raised wooden walkway through Cypress swamp in Fakahatchee strand, Florida, USA

DAVID TIPLING / Toursits watching birds through binoculars from canopy walkway, foothill rainforest, El Valle, Panama.

DAVID TIPLING / Toursits watching birds through binoculars from canopy walkway, foothill rainforest, El Valle, Panama.

DAVID TIPLING / Toursits watching birds through binoculars from canopy walkway, foothill rainforest, El Valle, Panama.

DAVID TIPLING / Walkway across phragmites reed bed, Arundel WWT, Sussex, UK

Jose B. Ruiz / Wooden walkway across sand dunes, Cape Peninsula, Cape of Good Hope, South Africa.

DAVID TIPLING / Lowland heathland landscape at Arne RSPB reserve, Dorset, UK.

Jose B. Ruiz / Walkway in Tablas de Daimiel National Park, Ciudad real, Spain.

Jose B. Ruiz / Walkway in Tablas de Daimiel National Park, Ciudad real, Spain

Igor Shpilenok / Boardwalk path trail winding through dwarf Alder {Alnus fruticosa} stand, Valley of the Geysers, Kronotsky Zapovednik Reserve, Russia.

Juergen Freund / Aerial roots of the Curtain fig tree {Ficus sp} Atherton Tablelands, Yungaburra, Queensland, Australia

Juergen Freund / Shark in Reef Headquarters Aquarium, Townsville, Queensland, Australia

Philippe Clement / Tourists on walkway through Porcelain Basin, part of the Norris Geyser Basin, Yellowstone NP, Wyoming, USA

Philippe Clement / Tourists on walkway through Porcelain Basin, part of the Norris Geyser Basin, Yellowstone NP, Wyoming, USA

Philippe Clement / Tourists on walkway through Porcelain Basin, part of the Norris Geyser Basin, Yellowstone NP, Wyoming, USA

Rolf Nussbaumer / Bridge at Cascade Creek, Jenny Lake, Grand Teton National Park, Wyoming, USA

Fabio Liverani / Rainforest canopy skywalk, Monteverde NR, Costa Rica

Daniel Gomez / Forest canopy walkway in Ulu Temburong NP. Sultanate of Brunei, Borneo.

Pete Oxford / Man on boardwalk through rainforest, Sacha Lodge, Amazonia, Ecuador.

Pete Oxford / Boardwalk through rainforest, Sacha Lodge, Amazonia, Ecuador

Philippe Clement / Tourists on boardwalk looking at thermophile mats, formed by algae, bacteria and other heat loving micro-organisms, Black Sand Basin, Yellowstone

Mark Raycroft / Pug (Canis familiaris) sitting on walkway

Konrad Wothe / Suspension bridge in Abel Tasman National Park, South Island, New Zealand

Mark Moffett / Tourists in rainforest walkway at Pouring Hot Springs near M. Kinabalu, Sabah, Borneo

Mark Moffett / Researchers suspended in gondola from crane's 280 foot arm over canopy, Wind River, Washington

Pete Oxford / Canopy walkway. The Amazon, Ecuador, South America

Jose B. Ruiz / Walkway in Tablas de Daniel NP, Cuidad Real, Spain, Europe.

Martin Gabriel / Canopy walkway through Eucalyptus forest, Valley of the Giants, Western Australia

Nick Gordon / Community near Santarem in Varzea, Amazon River flood plain, with walkway over water to houses and church.

Norbert Wu / Boardwalk through coastal dunes, Asilomar State Beach, Pacific Grove, California

Chien Lee / Canopy walk through lowland rainforest, Danum Valley Conservation Area, Sabah, Borneo, Malaysia

Roberto Rinaldi / Predator Lagoon aquarium tunnel, Atlantis, Paradise Island, Bahamas.

Mark Moffett / Lesser Woodcreeper (Xiphorhynchus fuscus) held in the right hand of Ornithologist Paulo Cordeiro and a White-shouldered Fire-eye (Pyriglena leucoptera) is held in his left, Una Ecopark, Atlantic Fores...