quality:correction, structural:summarization, linguistic:paraphrasing
Design

Borobudur is built as a single large stupa and, when viewed from above, takes the form of a giant tantric Buddhist mandala, simultaneously representing the Buddhist cosmology and the nature of mind. Some scholars reject the idea that it is a mandala because, in their view, no evidence is present to suggest that the Shailendras were followers of Tantric or Vajrayana Buddhism. Moreover, the Buddhas of the Borobudur do not identify as the Five Tathagatas. The original foundation is a square, approximately 118 metres (387 ft) on each side. It has nine platforms, of which the lower six are square and the upper three are circular. The upper platform contains seventy-two small stupas surrounding one large central stupa. Each stupa is bell-shaped and pierced by numerous decorative openings. Statues of the Buddha sit inside the pierced enclosures.

The design of Borobudur took the form of a step pyramid. Previously, the prehistoric Austronesian megalithic culture in Indonesia had constructed several earth mounds and stone step pyramid structures called punden berundak as discovered in Pangguyangan site near Cisolok and in Cipari near Kuningan. The construction of stone pyramids is based on native beliefs that mountains and high places are the abode of ancestral spirits or hyangs.

The monument's three divisions symbolize the three "realms" of Buddhist cosmology, namely Kamadhatu (the world of desires), Rupadhatu (the world of forms), and finally Arupadhatu (the formless world). Ordinary sentient beings live out their lives on the lowest level, the realm of desire. Those who have burnt out all desire for continued existence leave the world of desire and live in the world on the level of form alone: they see forms but are not drawn to them. Finally, full Buddhas go beyond even form and experience reality at its purest, most fundamental level, the formless ocean of nirvāṇa. The liberation from the cycle of saṃsāra where the enlightened seeker is no longer attached to worldly form corresponds to the concept of sūnyatā, the complete voidness or the nonexistence of the self. Kāmadhātu is represented by the base, Rupadhatu by the five square platforms (the body), and Arupadhatu by the three circular platforms and the large topmost stupa. The architectural features between the three stages have metaphorical differences. For instance, square and detailed decorations in the Rupadhatu disappear into plain circular platforms in the Arupadhatu to represent how the world of forms—where men are still attached with forms and names—changes into the world of the formless.

Congregational worship in Borobudur is performed in a walking pilgrimage. Pilgrims are guided by the system of staircases and corridors ascending to the top platform. Each platform represents one stage of enlightenment. The path that guides pilgrims was designed to symbolize Buddhist cosmology.

In 1885, a hidden structure under the base was accidentally discovered. The "hidden footing" contains reliefs, 160 of which depict narratives describing the world of desires. The remaining reliefs are panels with short inscriptions that apparently provide instructions for the sculptors, illustrating the scenes to be carved. The real base is hidden by an encasement base, the purpose of which remains a mystery. It was first thought that the real base had to be covered to prevent a disastrous subsidence of the monument into the hill. There is another theory that the encasement base was added because the original hidden footing was incorrectly designed, according to Vastu Shastra, the Indian ancient book about architecture and town planning. Regardless of why it was commissioned, the encasement base was built with detailed and meticulous design and with aesthetic and religious consideration.