There is no direct public bus service to Refugio de El Pilar. The nearest bus stops require taking a local taxi or hiking up via road LP-301:
From Caldera Visitor Center (El Paso): ~13.5 km / 8.4 mi (15–20 min drive/taxi).
From San Isidro (Breña Alta): ~11.5 km / 7.1 mi (15–20 min drive/taxi).
On foot: Hikers can ascend from San Isidro following the official PR LP 18 trail (+1,400 m elevation gain).