Mangku Mokoh took the daring snap after scaling Mount Agung, which is expected to erupt at any moment.
The photo, which has been shared thousands of times on social media, shows him sitting calmly on the edge of the crater while steam rises behind him.
He even took a video of the crater, which is belching smoke into the atmosphere through cracks in its surface.
A number of priests have also scaled the volcano over the past 24 hours to make offerings.
Their actions have sparked scathing criticism from officials who warned people to avoid the mountain until it is declared safe.
Mount Agung has been shaking throughout September, with fears it could erupt at any moment.
After tremors were sent through the area and the menacing volcano began spewing white smoke into the air, its alert status was raised to the highest level last week.
Around 144,000 people have evacuated their homes after a danger zone was set up around the volcano
The national disaster management agency said many people fled from local villages because they are unsure of their proximity to the 12km exclusion zone.
Evacuees are being housed in tents, school gyms, and government buildings in neighbouring villages.
While there are plentiful stocks of food, water, medicines, and other supplies, evacuees fear they are in for a long wait that could disrupt their livelihoods.
One farmer said he was worried that lava flows could destroy his house and farm.
Gusti Gege Astana, 40, said: ”If my house is destroyed I don’t know how to restart my life. I don’t know where my kids will sleep and all I can do now is pray.”
More than 1,000 people were killed the last time Mount Agung erupted, in 1963.
An elderly woman who survived that eruption said evacuation instructions had come much earlier this time.
Gusti Ayu Wati, 82, said: ”Back then we weren’t evacuated until it got really dangerous. Life went on as normal when ash and gravel was falling on us, until the big lava came out and destroyed everything.”
Indonesia has nearly 130 active volcanoes, more than any other country.
Many of these show high levels of activity but it can be weeks or even months before an actual eruption.