Writing that "The Observatory have outdone themselves this time", X' Ho reviewed "Catacombs" by declaring, "Someday in the future, some pop historian is gonna look back and say – "Catacombs" marks the beginning of a new horizon in local music for the sheer fact that waywardness in Singapore's ultra-leftfield, alternative-rock has been deemed fetching and unanimously praised with this album." Critic Kevin Mathews praised "Catacombs" by calling it "an uncompromising honest work of art that expresses the deepest feelings and emotions of the artist and lays them bare for its audience to dissect, absorb and devour." "my Paper" described "Catacombs" as "dark, visceral and multi-faceted", promising that it will "get under your skin – and stay there." Yeow Kai Chai of "The Straits Times" awarded the album four out of five stars, comparing it to late Scott Walker and noting lyricist Leslie Low's references to Dutch occultist Johann Weyer and French philosopher Michel Foucault, writing that "the band have moved out of the mainstream into the furthest frontiers of the universe." Alia Azmi of "Juice" magazine noted that the album "explores a deeper, heavier sound than their previous works". In 2017, music website "Bandwagon" ranked "Catacombs" as the best The Observatory album, writing that "it stands as the band’s crowning achievement in framing primal emotions within intricate instrumentation...an incredible singular statement of artful intention and uninhibited honesty".