Food waste and litter were left strewn across the ground at one of the entrances to Rivington Terraced Gardens.
It is believed that a potential stag-do may have been responsible for the mess. According to volunteers, it appeared that someone had been tied to a gate and then had eggs and flour hurled at them.
About 100 people came across the mess as they arrived at about 9.15am on Saturday for a monthly conservation effort and guided walk.
Volunteers are now faced with clearing up the refuse from the gated access at Lower House car park, off Sheepfoot Lane.
The site is currently the focus of a multi-million-pound Heritage Lottery project, led by the Rivington Heritage Trust (RHT) in partnership with Groundwork, to restore the grounds.
Andrew Suter, Groundwork’s project manager, said: "Collectively about 100 of us turned up to find a complete mess. It is really frustrating. It is disgusting.
"It looks like someone has had a stag-do. They have used cable ties and tape, presumably to tie someone to the gate and then thrown loads of eggs and flour at them.
"We had arrived to have a really positive day and make some improvements at the gardens. But instead, we will end up having to clean up this mess."
Between 15 and 20 bags of flour were left behind, as well as empty bottles, boxes of eggs and kitchen roll.
The remains of dozens of cracked eggs were also splattered across the ground and gate.
Mr Suter said: "Unfortunately this group of people has shown no respect for the gardens. They have shown no sense of right or wrong.
"If you are going to come to Rivington, please have a lovely time and enjoy yourselves, but please take your waste home.
"If you see anything untoward happening in the gardens, please report it to us."