To link phrases and describe a location (like "the city in which the headquarters is located"), you need a relative pronoun.
After a short preposition in Spanish (like en, desde, or por), use a complex relative pronoun: a definite article (el, la, los, las) plus que. The article must match the gender and number of the noun it refers back to.
| This is the venue in which the band was going to play. | Este es el recinto en el que iba a tocar la banda. |
| The city in which the headquarters is located is very big. | La ciudad en la que está la sede es muy grande. |
Movement and direction
You will frequently see this structure with prepositions indicating movement or routes, such as por (through, along) or a (to).
| The stretch through which the train was going was very dark. | El tramo por el que iba el tren era muy oscuro. |
| The summit to which we were going was as white as ice. | La cumbre a la que íbamos era tan blanca como el hielo. |
Formal contexts and "el cual"
For a more formal tone, you can swap que for cual (el cual, la cual, los cuales, las cuales). It translates exactly the same way as el que, but is often preferred in formal writing.
| which / who (relative pronoun) | cual |
| We arrived at the viewpoint, from which the landscape was incredible. | Llegamos al mirador, desde el cual el paisaje era increíble. |
Compound prepositions
El cual is also the standard choice after longer, multi-word prepositions, such as alrededor de (around) or debajo de (under). Notice how the preposition de combines with the article el to form del cual.
| We saw the venue, around which there were many trees. | Vimos el recinto, alrededor del cual había muchos árboles. |
| We entered the bank, under which there is an old vault. | Entramos al banco, debajo del cual hay una bóveda antigua. |