데 is the plain word for 'place', with a describing clause in front: 여기 괜찮은 데 있어? 'is there a decent place around here?'. It also simply says where someone is: 추운 데 있을 때는 하루 종일 누워 있고 'when he's somewhere cold he lies down all day'. Watch 같은 데, which does two jobs — 발리 같은 데 'places like Bali', but 모모가 같은 데 있네요 'Momo is in the same area'. Of a person's body, 안 좋은 데 있다 means something is wrong somewhere.