An annual gathering to celebrate a traditional spirit-god in one of Nigeria's few remaining virgin forests is one of the last places you would expect to hear complaints of over-commercialisation.
But experts on Nigeria's traditional religion say the 600-year-old Osun-Osogbo Sacred Grove Festival is under threat.
The event is now sponsored by international phone company MTN, Star beer, and Seaman's Schnapps, an alcoholic drink that touts itself as the "number one prayer libation drink".
Devotees believe that the sacred grove is one of the last remaining places that the spirits, or "orishas" will reveal themselves.
If the spirits decide not to come, the festival will die, they say.
Traditional beliefs involving animist spirits are still widely held in Nigeria, by people who say they are Christians and Muslims alike.
Each devotee family has a specific orisha, who their members will worship for the whole of their lives, but people also make offerings and sacrifices to other spirits who have responsibility for different aspects of life, hoping for their blessing.
Sacrifices can include killing chickens or rams, or token offerings like kola nuts, or libations of alcohol poured on a shrine.
The popularity of the festival has increased dramatically over the last 30 years, mostly due to the dedication of Austrian-born artist Susanne Wenger, who rebuilt the shrines and worked to get the grove protected.
Financial trouble in the last eight years has led organisers to turn to commercial sponsors for funding.
"These people have their own targets and that is to make their own money," says artist and expert on orisha worship Ajani Adigun Davies.
"They want to bring more people here, especially from abroad, they will bring their own culture to the festival and it will take over."
The annual festival was started by the founders of the town of Osogbo around 600 years ago, who meant to build their houses by the river bank.
As they began felling trees, it is said the spirit of the river-god Osun called out to them, ordering them away.
The grove has been a sacred area of worship for the spirit's devotees ever since.
Christian missionaries tried to stamp out animist beliefs while Nigeria was under British rule.
Rituals involved with orisha worship at that time included human sacrifice, which was stopped by the authorities.
The festival dwindled to only a few thousand worshippers, Mr Adigun Davies says.
But since the 1980s, the festival's popularity has been growing once more.
Mrs Wenger's renovation of the grove, which was protected by the state government in 1979, drew devotees back to the festival.
In 2003, the sacred grove, the last remaining 67 acres of virgin forest in the area, was recognised by Unesco as a world heritage site.
But at the same time, organisers were having trouble raising enough money from the local devotees to keep the festival running.
"Now we're making so much money that the organisation is no longer a problem," said Ayo Olumoko, of festival marketing consultants Infogem.
He disagrees that the commercial sponsorship will harm the spirit of the festival.
"If you want commercial entities to come and bring in their money, they must be allowed to showcase their wares," he says.
One of the sponsors of the festival, Seaman's Schnapps, said their product was absolutely central to the devotees' relationship with the spirit world.
"When they use Seaman's, over time, it has been proved that it serves as a conveyor of original blessings for them," said Bolaje Alalade, promotions manager for Seaman's Schnapps
"When they use this drink, it delivers their expectations."
The drink even comes in handy plastic sachets - just enough for a single libation.
Mr Olumoko said the idea to market products at the festival had not come up during the time Mrs Wenger was involved in managing the festival.
But she took a back seat in 2004, due to her increasing old age.
The marketers are trying to attract international tourists to the festival.
There are deities whose devotees are banned from drinking alcohol and it is not right that it is advertised in the grove, Mr Adigun Davies says.
"Susanne hates the sponsorship, she fought it all of the time that she was in charge, and it is only now she is old and cannot fight it any more that it has come up."
Mr Adigun Davies resigned as the curator of the grove because he was frustrated at the attempts by government to modernise the festival grounds to make access easier.
Artists in Mrs Wenger's Sacred Arts group agree that bringing more non-believing onlookers, especially foreign ones, is bad for the spirituality of the festival.
Metal sculptor Ajibike Ogunyeli makes statuettes of spirits from scrap metal.
His work is inspired by his childhood sightings of spirits in the grove.
"But since the Europeans started coming to the festival, all the spirits have disappeared," he said.
Osogbo's artists have seen their artwork go on sale in galleries throughout Europe and their livelihoods boosted.
They would undoubtedly get more money from an increase in curious tourists coming to the area.
But they do not want to do it at the expense of their own culture.
"I like the money that comes in and makes the festival happen," said Mr Adigun Davies.
"But the money will bring in negative impacts, they will say: 'We need some hotels here', or 'Let's have rest areas here, fast food joints', and before you know it they are taking down trees for a car park."
"It will happen, just watch."