A man climbed on top of a cathedral altar after pulling down his trousers, broke a crucifix and punched a 70-year-old woman in the face, a court has heard.
Nicholas Courtney, 34, claims he walked into Exeter Cathedral to pray before being overcome by the urge to "give everything to God".
He placed £20 in a donation box by the high altar, before stripping off his trousers - exposing his buttocks to horrified worshippers and visitors.
Courtney then ran to the cathedral's high altar and jumped on top of it, causing a cloth covering it and two candle sticks to come crashing to the ground.
Exeter Crown Court heard Courtney leapt off the altar and broke a crucifix, before fleeing by the cathedral's west exit.
He first smacked an outraged onlooker after she began reprimanding him but became angry when she hit him back.
Courtney next targeted a frail 70-year-old woman, who was posing for a picture with her young grandchildren outside the cathedral ahead of her fourth course of chemotherapy.
He punched her in her right eye, causing the grandmother to fall to the ground and break her wrist.
Stunned members of the public outside the cathedral were able to pin Courtney down and restrain him until police arrived.
Tattooed Courtney later pleaded guilty to charges of criminal damage and inflicting grievous bodily harm.
He will be sentenced at a later date.
Judge Jeremy Griggs warned the offences were so serious they required a "substantial custodial sentence".
Prosecuting, Nigel Wraith said Courtney, of Exeter, had walked into the cathedral at around 1pm on February 15, without paying the entrance fee.
"He walked up to the altar and placed some money, £20, on top of the donation box," he said.
"He then started removing his clothing.
"He removed his trousers, he exposed his buttocks.
"Cathedral employees spoke to him and managed to persuade him to replace his clothing.
"He then ran to the high altar, climbed on top of it, pulled the cloth off it, chucking off two candle sticks in the process.
"He then jumped off the altar, causing further damage to a crucifix."
Mr Wraith said cathedral staff later told police they felt "outraged and alarmed" by Courtney's behaviour.
He described how a 70-year-old woman had been posing for pictures with her grandchildren, aged three and five, on the cathedral steps.
Mr Wraith said: "Her husband was taking a picture of her and her grandchildren when she suddenly felt a punch.
"A fist hit her hard in her right eye and it was forceful enough to strike her off her feet."
The woman, who was terminally ill with cancer from a tumour in her back, put her left arm out to break her fall, causing her wrist to fracture.
Mr Wraith said the woman was due to undergo her fourth course of chemotherapy and it was not clear whether her injuries sustained in the attack would affect her treatment.
Police rushed to the scene and arrested Courtney who said: "Oh God, what have I done?
"I can't come back here, I will get a kicking.
"This is God's waiting room, isn't it?"
In interview, Courtney told officers he went to the cathedral to pray but "lost it" when he arrived, for some unknown reason.
He claimed he climbed on to the altar to be "closer to God", Mr Wraith said.
Courtney claimed he attacked the grandmother following an altercation with a younger woman, who hit him after he struck her first.
Mr Wraith said: "She had complained to him about the fact he had hit her hard.
"He had then seen the victim, who he described as an old lady in a long coat.
"He thought to himself 'I bet she can take a harder punch then that girl'."
Defending Courtney, Jeremy Harris said Courtney had been prescribed treatment for mental health problems but did not take it and had instead been self-medicating with legal highs.
Mr Harris said: "He is totally appalled, he is deeply remorseful for his actions.
"He describes his actions as despicable and totally beyond reason."
Judge Griggs remanded Courtney in custody and adjourned the case for medical reports to be carried out.
"Having considered what has been said on your behalf, having read the pre-sentence report, having heard the circumstances of what happened I am entirely satisfied that before sentence the court would want to know more about your mental background and your mental state," the judge said.
Courtney will be sentenced at Exeter Crown Court on June 6.