Top rests on the base, it doesn't particularly snap into place. Entrance seems a bit small, even my smaller cat seemed hesitant about entering. Took the cats about 5-7 days to learn to maneuver inside; until then, urine was ending up on the inner steps where there is no litter (that's not this particular product's design flaw, just something to be aware of with this style). Overall not bad, not amazing, but a decent price for something you probably want to replace every now and then.