To the east, there is the main garbhagriha (sanctum sanctorum) accessible via the antarala (vestibule or antechamber). The dvarashakha (doorframe) of this sanctum is crafted by featuring multiple sections and adorned with sculptures of davarapalas (door guardians) and women holding kalashas (pitchers). Although the lalatabimba (lintel) of the doorframe displays a seated figure, its condition is not well preserved. Positioned above the lintel, the entablature showcases Natesha at the center.
The garbhagriha (sanctum sanctorum) of the Undeshwar Temple is a compact square chamber positioned 2.4 meters below the floor level of the mandapa (pillared hall). Access to the garbhagriha is facilitated by a flight of steps. Positioned at the center of the garbhagriha is a Shiva linga (aniconic representation of Shiva). The walls of the garbhagriha are unadorned and lack any ornamentation or figurative representation.
On the steps and platform of the Mandakini Kund, several inscriptions are discovered in various states of preservation. These inscriptions are written in the Sanskrit language using the Devanagari script. A thorough examination of these inscriptions reveals valuable information, including the name of the temple, Mahakal, and the designation of the reservoir as Mandakini. Additionally, they provide details such as the date of the devotees' visit and their community affiliation. The inscriptions mention the worshipers' practice of visiting the Mahakal Temple and bathing in the Mandakini Kund. Dating from the 13th to the 15th centuries CE, some of these inscriptions specifically mention members of the Kayastha Mathur community.
The jangha (wall) of the garbhagriha (sanctum sanctorum) of the Hazareshwar Temple is adorned with sculptures depicting the trinity within bhadra (central offset) niches. On the southern bhadra of the jangha, Nataraja is depicted. Nataraja is portrayed in an urdhvajanu (with raised knees) posture, holding various weapons and attributes, including a sarpa (serpant), a damaru (double-headed drum), and a pointed weapon, possibly a shula or a trishula (trident). His frontal right hand is raised near his face, while in his left hand, he holds a khatvanga (staff with a skull), with the other left hand being damaged. Using his front left hand, he makes the gajahasta (elephant trunk gesture).
The western side of the southern garbhagriha (sanctum sanctorum) of the Mahakal Temple features a bhadra (central offset) adorned with a jali (lattice) window. The rectangular frame of this window is embellished with a motif resembling a four-petaled flower.
The Undeshwar Temple follows a Saparatha (seven projections on all four sides) architectural plan and consists of a mukhamandapa (front porch), mandapa (pillared hall) with extensions on the north and south sides, an antarala (vestibule or antechamber), and garbhagriha (sanctum sanctorum).
The superstructure of the southern garbhagriha (sanctum sanctorum) is shekhari in style i.e., the central latina spires with rows of half spires added on either side. It comprises a mulamanjri (principal spire), uruh shringas (subsidiary spires leaning against the main spire), and shringas (miniature shrines). Divine figures adorn the shikhara's surface.
Similar to the southern garbhagriha (sanctum sanctorum) of the Mahakal Temple, the eastern garbhagriha also features a vedibandha (basal mouldings), jangha (wall) and shikhara (superstructure) in shekhari style. The vedibandha includes khura (hoof), kapotapalika (cyma recta), kumbha (pot), and kalasha (pitcher) mouldings. While the jangha remains entirely plain without any sculptural embellishments, the shikhara of the garbhagriha displays divine figures.
Inside the enclosure walls, numerous sculptures are displayed, including depictions of goddesses, deities such as Brahma, Vishnu, and Mahesha, dikapalas (deities for cardinal directions), surasundaris (celestial damsels) and vyalas (mythical composite creatures). They are arranged sporadically, lacking a clear order or sequence, indicating that they were not initially intended to decorate the reservoir.
The kumbha (pot) molding of the vedibandha (basal mouldings) stands out due to its depiction of divine figures within the niches, featuring gods and goddesses like Kubera, the deity associated with wealth. Notably, the top of the kumbha is adorned with a chaitya arch, a feature commonly found on kapotapalika (cyma recta) moldings. Below the kumbha, there is a band showcasing kirtimukha (face of glory) motifs, while above the kumbha, the molding of kalasha (pitcher) is intricately carved with ratnapatta motifs.