The remarkable subterranean growth habit of Nepenthes rhombicaulis is described based on the examination of nine mature plants in the UK’s National Plant Collection of Nepenthes at Chester Zoo. The species is found to produce most of its pitchers below ground, these being larger and sturdier than—and morphologically distinct from—its more familiar aboveground traps. The underground pitchers are borne on vertically orientated stems originating below the soil line, which are only transiently carnivorous and eventually develop into pitcherless lianas. As such, repeated subterranean branching is necessary to sustain concealed carnivory. Underground pitchers appear to have lengthy functional lifespans, likely reflecting their increased construction costs. The consistent production of plentiful underground pitchers even under conditions of artificially high light abundance points to the phenomenon being a genetically determined adaptation rather than a plastic response to shading. Suggestions are made for how to cultivate and display this unusual species to best effect.