There are probably several hundred sludge-metal bands right now churning out charcoal soot–encrusted streams on Bandcamp and playing tiny basement bars that reek of stale beer, their setlists culminating with Motörhead covers that sound more like Eyehategod or maybe the other way around. Ilsa, having formed a decade ago, has helped influence this new generation of gutter snipes by virtue of longevity as well as prolificacy: they’ve averaged a new full-length every two years alongside splits with the likes of Hooded Menace and Seven Sisters of Sleep.

Corpse Fortress is the band’s fifth album and notably its first for Relapse Records. This pairing with the semi–major label seems overdue as all of their splits were with Relapse artists, including the last one with Coffins in 2016. However, signing with the label hasn’t changed how the band operates in any meaningful way. As in the past, they recorded the new record with Kevin Bernsten (Full of Hell, Code Orange, Magrudergrind, Integrity) at Developing Nations studio in nearby Baltimore. The album cover, a wailing mask surrounded by creepy insects, is a black-and-white drawing by drummer Joshy Brettell, who has done all of the band’s artwork. (He also drums in Integrity, whose last album also came out on Relapse.)

Lead track “Hikikomori” sees the band culminating the past 10 years into one song. Over Brontosaurian riffs, burly bearded vocalist Orion Peter belches out, “Spend my life in low-lit rooms, nursing sour beer… Soaked in sludge, hair down to my knees.” The cut stands out from the rest of the album not just because it’s the only occasion where the band keeps it real (elsewhere, Ilsa explores time-honored themes of horror and hellfire), but it’s the most traditionally doom moment of the record. Sludge and doom often seem intrinsically intertwined, but favoring the former, the sound on Corpse Fortress is raw and dirty. “Cosmos Antinomos” is dirgy D-Beat; “Prosector” could be a Fear, Emptiness, Despair–era Napalm Death B-side if the band was on Novocain at the time; and “Old Maid” is like a slowed-down Nausea track, thanks to a crusty rhythm and shrieking vocal accompaniment from DC documentarian Amy KC Oden.

Corpse Fortress is a slovenly slab of sludge that’s grimy enough to make the crust punks think they’re the ones being serenaded. Instead of going nowhere fast, though, Ilsa goes a few different places very slowly. It makes for quite the trip.