Learn Spanish (Latin America): Vimos el recinto, alrededor del cual había muchos árboles. - We saw the venue, around which there were many trees.

While you could technically use del que, el cual (and its forms) is highly preferred after compound prepositions. These are prepositions made of two or more words, like alrededor de (around) or debajo de (underneath). Using el cual in these cases sounds much more natural and clear in written or careful speech.

If the relative pronoun is el cual, why does the sentence use del cual?

The phrase for 'around' is alrededor de. The relative pronoun matching el recinto (masculine singular) is el cual. In Spanish, the preposition de and the masculine article el must always contract to form del. This rule applies even when they are part of a complex relative pronoun, making the final phrase alrededor del cual.

Why is 'there were' translated as había (imperfect) rather than hubo (preterite)?

We use the imperfect había because this is a background description. The main completed action in the past is Vimos (we saw). The trees simply existing around the venue is an ongoing state or setting at that exact moment, which requires the imperfect tense.

What exactly does recinto mean? Is it always a 'venue'?