The hidden reliefs depict the Karmawibhangga -- the Buddhist law of cause and effect as described in the realm of desire, or Kamadhatu. Unlike the narrative panels on Borobudur's upper galleries, which tell continuous stories of the Buddha's life and Sudhana's spiritual journey, these 160 panels each stand alone. Every frame is a self-contained moral lesson. Fishermen hauling nets in one scene are shown being boiled alive by demons in the next, their livelihood recast as karmic transgression. Scenes of adultery lead to scandal; scenes of charity lead to paradise. The carvings depict torture, bondage, burning, and dismemberment alongside agricultural cooperation, pilgrimage, and planned parenthood. Some panels carry inscriptions that appear to be instructions to the carvers themselves, and several remain unfinished -- a detail that has led scholars to theorize the encasement was added before the temple was even complete.

The museum building itself is a study in Javanese architectural tradition. Designed as a joglo -- the classic Central Javanese house form with a dramatically peaked roof supported by four central pillars -- it features an open pendopo pavilion at its entrance, the kind of structure traditionally used for receiving guests and holding ceremonies. Inaugurated in 1983 as part of the Borobudur Archaeological Park that followed the massive UNESCO restoration, the museum was conceived not just as a gallery but as an educational tool. Its exhibits trace the entire restoration project undertaken between 1975 and 1982: old photographs, maps, models of interlocking stone structures, and displays explaining the conservation challenges that nearly destroyed Borobudur -- fungal growth, moss, drainage failures, and the slow chemical decay of andesite stone exposed to tropical weather for centuries.

Beyond the photographs of hidden reliefs, the museum houses archaeological artifacts excavated during Borobudur's multiple restoration campaigns. Terracotta water vessels, ceramic containers, and storage jars unearthed from the soil around the temple offer glimpses of daily life during Borobudur's active centuries. One of the most striking exhibits is a large 9th-century Buddha head discovered not at Borobudur itself but in Selomerto, in the neighboring Wonosobo Regency -- evidence that the Buddhist artistic tradition extended well beyond the temple complex. The museum also displays disassembled Borobudur stones, including fragments that help visitors understand the monument's construction: how the stones were cut, transported, and fitted together without mortar. The chattra -- the three-tiered parasol pinnacle that once topped Borobudur's main stupa, partially reconstructed and then dismantled by Dutch engineer Van Erp in 1911 because too few original stones could be confirmed -- is stored here as well, awaiting a decision about its future.

The Karmawibhangga Museum shares the Borobudur Archaeological Park with the Samudra Raksa Museum, located directly to its west. Where Karmawibhangga looks inward -- at the spiritual and structural secrets of the temple itself -- Samudra Raksa looks outward, displaying a full-scale replica of the Borobudur Ship, an 8th-century double-outrigger vessel depicted in the temple's relief panels. That replica sailed from Indonesia to Madagascar and then to Africa in 2004, retracing ancient maritime trade routes. Together, the two museums frame Borobudur as both a spiritual monument and a product of a sophisticated maritime civilization that traded across the Indian Ocean. Entry to both is included in the Borobudur Archaeological Park ticket, and yet many visitors bypass them entirely in their rush to climb the temple -- missing, ironically, the very things that explain what they are climbing.