There are good reasons we don't see land dwelling arthropods any larger than 15-20 centimeter leg span (for insects and spiders) or up to about 50% above that (for exceptional crabs, like tree-climbing coconut crabs).
That reason is the square-cube law.
If you double the size (linear dimension -- height, leg span, etc.) of an arthropod, you quadruple its strength, but you octuple its weight -- and with the muscles trapped inside the exoskeleton, they can only get so strong. Worse, the exoskeleton is an inefficient way to get bone strength; you gain more weight for a given amount of added cross section area (=> strength) than you would for an internal skeleton like those of vertebrates.
Still worse, breathing apparatus gains effect on the square (the area exposed to air), while oxygen requirement goes on the cube (volume/mass of flesh to supply).
By the physics, it's my understanding that an arthropod dwelling largely on land simply can't get any bigger than about the size of a coconut crab, blue crab, or at most a dungeness crab (which, however, live in deep ocean). Horseshoe crabs get somewhat larger, but they don't leave the water often and have many more legs (and aren't really crabs at all).
So, far from being able to walk upside down on a suitably strong ceiling (cave roof?), your 60+ kg spider wouldn't even be able to walk upright on the ground -- it might not even be able to breathe in order to stay alive.
Now, move everything underwater, where the displaced water supports most of the animal's weight (and, surprisingly, breathing may actually be easier relative to size -- cold water can carry a lot of dissolved gases), and things get a lot more likely...