KOH KER · PREAH VIHEAR, CAMBODIA
Koh Ker Pyramid.
Sunrise on the Zenith Line.
The Prang at Koh Ker is the biggest pyramid in Cambodia, and the temples in front of it are lined up with sunrise on the zenith day. I climbed it by headlamp to watch that sunrise in April, then went back in June just to see the pyramid again.
MEC ZENITH TOUR + PRIVATE RETURN
VISITED APRIL + JUNE 2025 · KOH KER
THE SHORT VERSION
What is Koh Ker?
Koh Ker is a 10th-century Khmer capital about 120 km northeast of Siem Reap, in Preah Vihear province. For a short time under King Jayavarman IV it was the center of the Khmer Empire. Its centerpiece is the Prang: a seven-tier pyramid, 36 metres tall on a 62-metre base, the largest pyramid in Cambodia. Koh Ker became a UNESCO World Heritage Site in 2023.
Most Khmer temples face due east. The Prasat Thom complex in front of the Prang doesn’t. It’s turned 14° north of east, which is exactly where the sun rises on the zenith days, around April 27 and August 16.
Is Koh Ker worth the trip from Siem Reap?
Yes, if you like pyramids, ancient astronomy or just quieter temples. It’s a long drive, but it feels completely different from Angkor: fewer people, more forest, and you can climb all the way to the top of the pyramid.
For the sunrise you need to stay nearby the night before. For a daytime visit, a day trip from Siem Reap works fine. I’ve done both.
Koh Ker details
WHERE
Preah Vihear province, about 120 km northeast of Siem Reap
DRIVE
About 2 to 2½ hours each way by car
ENTRY
$15 ticket at the site, separate from the Angkor Pass*
HOURS
7:30 AM to 5:30 PM
THE PRANG
36 m tall, 62 m base, seven tiers, with wooden stairs to the top
BUILT
About 928 CE, under Jayavarman IV
ZENITH SUNRISE
Around April 27 and August 16, roughly 5:40 to 5:50 AM
WHERE I STAYED
I AM Resort Koh Ker, the night before the sunrise
*Fee and hours from Hello Angkor. I remember paying closer to $20 in June 2025, so check before you go. Getting on the pyramid before opening time needs advance permission, which our tour arranged.
THE CLIMB
APRIL 26 – 27, 2025 / INDOCHINA TIME
Up the pyramid
in the dark.
Sunrise on the zenith day is the reason the tour came to Koh Ker. Here’s how we got to the top in time.
APRIL 26, 2025 / THE NIGHT BEFORE
Sleep close to the pyramid.
This was part of Maya Exploration Center’s zenith sun tour, led by Luke Caverns with our local guides Kanha Phum and Bon Chem. The day before we watched the noon zenith at the Bayon, toured Beng Mealea, then drove on to Koh Ker.
Koh Ker is too far from Siem Reap to make it for sunrise, so we stayed nearby at I AM Resort Koh Ker: simple A-frame bungalows with a pool.
IF YOU WANT THE SUNRISE, BOOK A ROOM NEAR KOH KER.
APRIL 27, 2025 / 5:15 AM
Headlamps on.
We were up before 5 and walking a dirt trail through the forest by headlamp. Watch your feet: at one point a thick river of ants was marching across the path. Then the Prang appeared out of the dark, a huge stepped silhouette against a deep blue sky.
APRIL 27, 2025 / 5:20 AM
A lot of steps.
Then you climb. There are a lot of steps, and in the dark you only see what’s in your headlamp. The good news: the stairs are modern, wooden and well built, with landings along the way if you need a rest.
BRING A HEADLAMP SO BOTH HANDS ARE FREE FOR THE RAILS.
APRIL 27, 2025 / ZENITH SUNRISE
The sun on the line.
The sky went pink, then orange, and the sun came up out of a flat line of forest, just off the side of one of the two big door-jamb stones on top. I didn’t realize there was a right spot to stand. The alignment runs through the old doorway between those stones, and I was watching from the side.
FIELD NOTES
On top of
the Prang.
Once it was light, we had time to look around the summit. There’s not much left up there, but what is left tells a story.
Two stones and
a very big hole.
The two tall stones are the door jambs of whatever stood on top. Stand between them and you’re looking straight down the zenith sunrise line. Behind them is a deep shaft dug by looters hunting for tombs or offerings, now covered with a wooden grid. Up here there once stood a giant linga, about 4 metres tall, possibly the largest in Southeast Asia. It’s gone now.
THE SHAFT
Looted long ago.
Looking down into the shaft under the old summit pedestal.
THE VIEW
Proof I made it up.
Flat forest in every direction, which is exactly why the sunrise line works.
36 m
tall, the largest pyramid in Cambodia
14°
north of east, the Prasat Thom axis
Apr 27
and Aug 16, the zenith sunrise days
928
CE, when Jayavarman IV commissioned it
WHY SUNRISE?
A city lined up
with the sun.
Ed Barnhart of Maya Exploration Center wrote the paper on this: Zenith Passage Alignments at Koh Ker, published in the Journal of Astronomy in Culture in 2026. Here’s the short version.
The zenith is the day the sun passes directly overhead at noon. At Koh Ker’s latitude, about 13°45′ north, that happens around April 27 and August 16. On those mornings the sun rises 14° north of east, the same angle as the Prasat Thom complex. The Prang sits at the west end, so from the top you look out over the temples toward that sunrise.
Kanha was part of the story. In 2022 he scouted Koh Ker for Ed, found lodging, got permission from the provincial authorities for a pre-dawn climb, and sent back photos of the April sunrise. The forest had grown over Prasat Thom, so for the August zenith the team flew a drone behind the summit to photograph the sun rising between the door jambs.
It’s the same Kanha who guided my Bakong zenith visit and my Angkor bike tour.
THE GIANT LINGA
The 4-metre linga on top may have worked as a giant gnomon: at noon on the zenith day, it would cast no shadow at all. Koh Ker’s old name, Lingapura, means “Linga City.”
A HOLE IN THE ROOF
The main shrine of Prasat Thom has the same kind of zenith hole as Bakong, so on zenith day the noon sun shines straight down inside it.
NOT NEW YEAR
One theory ties the alignment to Khmer New Year in mid-April. Barnhart points out that in the 10th century Khmer New Year was in November or December, and the alignment matches April 27, not April 13.
The paper also links Koh Ker to zenith features at Prambanan and Borobudur in Java, where the first Khmer king, Jayavarman II, is said to have grown up.
JUNE 8, 2025 / BACK IN DAYLIGHT
Back just to see the pyramid.
In June I came back on my own with a private driver from Siem Reap. No sunrise this time. I just wanted to see the pyramid again in daylight and climb it without a headlamp.
In daylight you notice how much forest is around the Prang and how much work is going into Prasat Thom: scaffolding on the towers, trees growing over the walls, and a moat with a little boat on it. From the top, the zenith axis runs straight out in front of you as a red dirt path.
Near the base there’s a small shrine with a stone elephant, with incense burning.
BEFORE YOU GO
What I’d tell a friend.
Pick your Koh Ker.
For the zenith sunrise, stay the night nearby and go with a guide who can arrange early access. For the pyramid itself, a day trip from Siem Reap with a private driver is easy.
Bring a headlamp.
The trail and the stairs are pitch black before dawn. A headlamp keeps your hands free for the rails.
Find the doorway.
If you’re there on a zenith morning, stand between the two door-jamb stones on top. That’s where the line is. Learn from my mistake.
Remember to tip your guide accordingly.
Frequently asked QUESTIONS
Koh Ker FAQ.
What is Koh Ker?
A 10th-century Khmer capital about 120 km northeast of Siem Reap, known for the Prang, a 36-metre, seven-tier pyramid that is the largest in Cambodia. It became a UNESCO World Heritage Site in 2023.
Can you climb the Koh Ker pyramid?
Yes. A modern wooden staircase with handrails and rest landings runs up the east side to the summit.
When is the zenith sunrise at Koh Ker?
Around April 27 and August 16 each year, at roughly 5:40 to 5:50 AM. On those mornings the sun rises 14° north of east, in line with the Prasat Thom complex.
How far is Koh Ker from Siem Reap?
About 120 km northeast, roughly 2 to 2½ hours each way by car.
Is Koh Ker included in the Angkor Pass?
No. Koh Ker has its own ticket, listed at $15, bought at the site.
Can you watch sunrise from the top of the Koh Ker pyramid?
The site normally opens at 7:30 AM, so a sunrise climb needs advance permission. Our tour group arranged it through our local guide.
Where should I stay for the Koh Ker sunrise?
Somewhere close to Koh Ker, not Siem Reap. We stayed at I AM Resort Koh Ker the night before.
Who discovered the zenith alignment at Koh Ker?
Archaeoastronomer Giulio Magli first identified the alignment, and Ed Barnhart of Maya Exploration Center photographed and documented it from the top of the Prang.