Before they became the sort of international superstars who headline places like Red Rocks, the Lumineers played many an open mic at the intimate Meadowlark. Every Tuesday night from 9 p.m. until 12:30 a.m., the venue gives local singer-songwriters a chance to test out new material, refine older songs or just show people what they're made of during their fifteen-minute allotment. At the Meadowlark, you just might see — or be — the Next Big Thing.