The Temple of Seti I at Abydos, Ancient Egypt, holds so many halls and rooms, decorated with such exquisite reliefs that a full description on a website like this is rather futile. Take this as only a brief introduction to a location which was central for the religious life in ancient Egypt for more than three millennia, both for kings and commoners.
In the 19th Dynasty, Seti I and his son Ramesses II began to restore Abedjou to its former glory after the short downperiod under Akhenaten´s 18 year long rule. But Seti did more than that. He began to build what is maybe the most beautiful temple ever, in white limestone, to all gods and all former kings of Egypt and he placed it where there had been an eariler temple building and by a processional path, between the temple and the traditional 'tomb' of Wesir. This became a national shrine. The reason he chose to do this is probably that he sought to establish his line as having Divine right to the throne. His father, Ramesses I, was of low birth and had been raised to the office as vizier by Horemheb.
Plan of the temple area
The temple precinct is situated by a former canal which once connected to the Nile and it is more than likely that it was built on top of several earlier temple structures. There was a ramp, a terrace and two pylons which accessed two consecutive courtyards which are now mostly destroyed. To the left were rows of storage buildings.
In front of the temple Seti erected a memorial chapel to his own father, Ramesses I. On its walls are exquisite reliefs showing the Royal Family offering to the gods.
Plan of the Temple of Seti I

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1: First Pylons. 2: First Courtyard w Ablution wells. 3: Second Courtyard. 4: First Hypostyle Hall.
5: Second Hypostyle Hall. 6: Shrine of Seti I. 7: Shrine of Ptah.
8: Shrine of Re-Heurakhety. 9: Shrine of Amun-Re. 10: Shrine of Wesir.
11. Shrine of Aset. 12: Shrine of Heru. 13: Hall of Nefertem and Ptah-Sokar.
14: Hall of Kings. 15: Hall of Wesir.
16: Chapel of Heru.
17: Chapel of Wesir.
18: Chapel of Aset.
19: Second Hall of Wesir.
20: Hall of Barks
21: Butcher Hall.
Store rooms & service rooms.
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The seven chapels; from left to right:
Deified Seti I, Ptah, Re-Heruakhety, Amun, Wesir, Aset and Heru.
(Photo: Jon Bodsworth)
Each of these chapels are decorated with reliefs of extraordianry quality, depicting rituals which were performed during various festival days.
Looking into one of the chapels
(Photo: Steve Beikirch)
The great temple is dedicated not only to the deified Seti I, but to a line of deities; Wesir, Aset and Heru, Amun of Waset (Gr: Thebes), Ptah of Men-Nefer (Gr: Memphis) and Re of Iunu (Gr: Heliopolis). The reliefs in the temple are very well preserved and of highest quality and give valuable information about the daily rituals.
The two courtyards are mostly in ruins today. On a memory plaque it says that these pillars 'reached all the way to the sky'. The columns of the hypostyle halls (4,5) have been arranged to give easy access into the seven chapels (6-12). Behind these chapels there are another two, smaller hypostyle halls, (15) each with three chapels for Wesir, Aset and Heru, the three deities of Abedjou.

Chapel of Amun-Re: Veiled statue of Amun-Re carried on its
Barque in Festival Procession
(Photo: Raymond Montfort)
The King-List
From the second hypostyle hall (5) a long corridor runs, stretching 'local south'. This is the Hall of Kings, (14) which on its western wall bears cartouches of all the rulers from the 1st dynasty up to and including the rule of Seti I. More of this here.
This corridor leads to two more rooms which hold chapels for Nefertem and Ptah-Sokar, and sanctuaries where processional barks and ritual utensils were kept. Outside of the temple were widespread magasines and storehouses.
The hall of Ptah-Sokar and Nefertem.
(Photo: Jon Bodsworth)
More here about the Hypostyle Halls and the Kinglist
Sources:
Guide to Religious Ritual at Abydos - A. Rosalie David
The Ancient Egyptians; Religious Beliefs & Practices - A. Rosalie David
Cultural Atlas of Ancient Egypt - John Baines & Jaromir Malek
The Complete Temples of Ancient Egypt - Richard H. Wilkinson