Answer: "Wandering through the catacombs" is a gerund phrase.
Explanation: A gerund phrase is a phrase made up of a gerund, that is to say a non-finite form ending in -ing, and its modifiers. A gerund phrase always acts a noun. Moreover, it can play different syntactic functions in a sentence. In "My best friend and I enjoy wandering through the catacombs", "wandering through the catacombs" is a gerund phrase since it is made up of the gerund "wandering" and the prepositional phrase "through the catacombs", which is modifying the gerund. Furthermore, "wandering through the catacombs" is acting as a noun and is playing the function of direct object since it is the recipient of the transitive verb "enjoy".
