A mysterious table-topped mountain on the Venezuela-Brazil border that perplexed 19th century explorers and inspired "The Lost World" novel is attracting ever more modern-day adventurers. Once impenetrable to all but the Pemon indigenous people, now several thousand trekkers a year make the six-day hike across savannah, through rivers, and up a narrow path that scales the cliffs to Mount Roraima’s nearly 3,000-meter summit. While that is a boon to Venezuela's tottering tourism industry and brings revenues to local indigenous communities, it is also scattering a prehistoric landscape with unwanted litter and straining a delicate ecosystem.