Neutron stars are extremely compact
Neutron stars are extremely dense - they can be even denser than an atomic nucleus. Typically, they have the mass of one and a half suns, compactified into a sphere with a diameter no larger than that of Berlin. At this density, the mass of the Italian volcano Stromboli (see picture above), a mountain 924 metres high and with a base area of 12.6 square kilometres would be compactified into a cube with sides about three centimetres long. Such a cube is visible in the showcase on your right.