Catalonia is in Cabeza de Torro area and Occidental Grand is in Plaza Bavaro area. The distance is about 15 to 20 kilometers. The cab will take you about 20 to 25 dollars each way. You certainly can walk on the beach to get there, but make it a day trip
I recommend setting off early, and taking plenty of water. To make it back and forth, make it an overnight excursion and pack a tent