"The mountains are bounded by deep valleys to the north, east and south, and offer vast vistas over the rugged-canyon like lowlands below. The spectacular scenery of the Simien mountains is considered to rival the Grand Canyon (USA)." (OUV)

"eight steep sided gorges" (OUV)

Kuiseb Canyon

Contains one of the largest underground canyons in the world (AB ev)

Grand Canyon of Nuku Hiva

a narrow 80m-wide canyon, el Garganto de Diablo (UNEP-WCMC)

the canyons of Caleta, Jauco, Caletica, Maya, Río Seco, and Boca del Toro rivers (nomination file)

Grand Canyon of the Yellowstone

Aksu Canyon

The canyon of Tehuacán-Cuicatlán is a deep gorge surrounded by peaks more than 3,000 m high (AB ev)

the Chu-Ili mountain spur forms a canyon around the Tamgaly Gorge (AB ev)

Piccaninny Gorge

The Siq

Four smaller canyons

Talampaya Canyon

Melinau Gorge Canyon

Capertee Valley, "the world's second largest canyon"
See www.visitnsw.com

Rio delle Foglie/Bletterbach

"With swooping aerial footage and detailed close-ups, it reveals a landscape of canyons and caves, lakes and lagoons, rivers and rock masses"
See www.theguardian.com

Gorges du Tarn

Maligne Canyon

the spectacular canyon of the Manambolo river - Unesco website

The plateau is cut by deep valleys and canyons (OUV)

Vikos Gorge ("Vikos is listed as the world's "deepest relative to its width" gorge by the Guinness Book of Records among others." (Wiki)