"To hike through canyons" will be converted into a gerund phrase by changing the verb "to hike" into a verb that end in -ing.
So, To hike through canyons is strenuous activity becomes Hiking through canyons is a strenuous activity.
Gerund phrases starts with a gerund, or a word that ends in -ing. It is followed by other modifiers or objects. Gerund phrases function as nouns. So, they can be subjects, subject complements, or objects in the sentence.
gerund phrase - Hiking through canyons
gerund - hiking
serves as subject of the sentence.