When Nekajui, a Ritz-Carlton Reserve , opened on Costa Rica's Peninsula Papagayo last year, it quickly became inextricable from the tropical hillside it calls home. The property's 107 rooms and suites (and 36 residences) emerge organically from among the tropical forest, where howler monkeys' cries hang in the air and guests travel through the treetops by a suspended bridge. With views of the Pacific Ocean and access to abundant wildlife, Nekajui is a Venn diagram of the natural bounty and diverse beauty that has long drawn travelers to the country's northwestern coastline. A view of the Andaz property Daniel Morales Other hospitality brands have followed suit, turning the larger Peninsula Papagayo area and Playa Penca, just across the bay, into a bona fide luxury enclave. The Waldorf Astoria arrived on Playa Penca (a brand first in Costa Rica) last April with a multitiered pool and cenote-inspired spa. An ambitious 50-acre St.…