JW Marriott Grand Rapids is a downtown hotel on Louis Street NW beside the Grand River, home to Seraphina Spa. Non-guests can buy a day pass through ResortPass for the heated indoor pool, which has floor-to-ceiling windows over the city, plus a sauna and a steam room in the pool area. ResortPass lists the pool as open daily 8 AM to 7 PM; day-pass holders check in at the front desk with a photo ID.