Beginning in episode 3 of the first season of the original series, the Marshall family begins referring to their cave home as "the high bluff." High Bluff is a natural cave high in a cliff face, with holes for light and ventilation, and makes an adequate defensible position for avoiding dinosaur attacks. From the cave entrance the Marshalls can drive away Grumpy by driving a large stick into his mouth. This trick is repeated in multiple episodes (even using the same footage).
Several large stair step-like stone formations below it allow the Marshalls and various visitors to climb in and out of the cave; there is also a crevice in the rocks at the base of the cliff that is inaccessible to the large dinosaurs. Will defends himself against Grumpy's attack this way in the first episode, "Cha-ka."