Does the spa offer open-air massage treatments?

Yes. Marriott’s wellness content explicitly mentions “an open-air massage” in Thailand and “open-air treatments” at Phulay Bay, a Ritz-Carlton Reserve, which shows that open-air massage and treatment experiences are offered in the collection. The evidence does not confirm that Casa Monica Resort & Spa specifically offers them, but it does support the availability of open-air massage treatments in Marriott’s luxury wellness offerings.