Gerund use

Hola Valeriia

We don't normally use the present participle form (gerundio in Spanish) as it's used in English, for example in "hanging baskets", or "embarrasing mistake" or "loving dog", acting as adjectives; to describe these houses in Cuenca, we wouldn't say "las casas colgando" - however we are using "colgando" in this sentense in the text as part of a verbal structure that is omitted. I understand this may be confusing, but here it is as if we were saying "En Cuenca hay tres casas [que están] colgando de una roca" (In Cuenca there are three house [that are] hanging from a rock.)

If you see the title of this exercise with just the name and the adjective you can see that we are using the past participle "colgadas": "Las casas colgadas de Cuenca". 

I hope this clarified it.

Saludos

Inma