Lumajang is not one of Java's polished tourist towns. Its centre is practical and spread out, but the regency around it holds some of East Java's strongest volcanic scenery: huge waterfalls dropping from the Semeru foothills, farming villages on cool high slopes, and back-door views toward the Bromo caldera.
The reason to come is the western and northern countryside rather than the town itself. Tumpak Sewu Waterfall is the headline, a great curtain of water in a horseshoe canyon below Mount Semeru. Nearby Goa Tetes and Kapas Biru Waterfall make this one of Java's best waterfall clusters if you are willing to get wet and muddy.
Lumajang also gives access to Puncak B29, a high village viewpoint over Bromo's sea of sand from a less obvious angle than the standard Probolinggo route. It is still rural and weather-dependent, which is part of the appeal. Come with time, an early start, and shoes that can handle steep paths.