The Abbey's management have launched a website in partnership with children's activity camp provider Activate promoting the 12th-century castle and its grounds as a holiday resort and glamping site and are taking bookings from late May.
Yet they may have fallen foul of planning regulations which require an application to be submitted and permission obtained before a major change of land use can legally take place.
Gilling Castle was home to nearby Ampleforth College's prep school, St Martin's, until it closed in 2018 and junior pupils were moved to the main campus.
The site was put up for sale with an asking price of £3.5million but has now been taken off the market.
According to the new website, guests will be able to book tent pitches or stay in ready-erected yurts, one of two bunkhouses inside the castle or a lodge that sleeps up to 12 people.
They will have access to 200 acres of grounds, which have a private lake and woodland trails, and be able to use the school's old sports facilities, which include a tennis court and astroturf games area, as well as play at Ampleforth College's golf course. The site is being marketed mainly to families and bookings from groups of adults will not be accepted.
Local residents have expressed concerns that Ampleforth Abbey and Activate appear to be planning to operate the resort as soon as May 29, when the bunkhouses will open, as they fear noise disturbance in a rural area.
One said: "It all seems a bit chaotic with no consultation with local residents who are bothered by noise, barbecues, Covid guidelines etc.
"Gilling Castle is a Grade I-listed building and its Grade II-listed gardens are in a poor and possibly dangerous state with broken glass in old collapsing greenhouses, dangerous steps, exposed nails. Children will naturally want to explore these areas. It's not really been thought through at all."
A spokesperson for Ryedale Council said: “We can confirm that we are investigating a complaint regarding the possible use of land and buildings owned by Ampleforth Abbey in relation to a possible change of use for buildings and surrounding land.
“Our investigation is at the initial stages, so we haven't yet been able to establish whether or not a breach in planning has occurred. When our investigation has concluded we will publish our findings on our website.”
Ampleforth Abbey company secretary Liam Kelly said: "We can confirm that we are co-operating fully with Ryedale Council in their consideration of our intended use of Gilling Castle this summer”
Ampleforth Abbey has owned Gilling Castle since 1929. It was previously a country seat of the Viscounts Fairfax.
Since a child abuse scandal which resulted in the convictions of several former monks who taught at both the senior and junior schools, Ampleforth College and Ampleforth Abbey have separated themselves as legal entities. Gilling Castle has remained in Abbey rather than College ownership.