About 12,000 music fans will head to Festival No.6 for what will be the last edition “for the time being”.
The award-winning event has been held in Portmeirion, Gwynedd, since 2012, and has attracted acts including Manic Street Preachers and Nile Rodgers.
It runs from Friday until Sunday, with headliners this year including Franz Ferdinand and Jessie Ware.
While describing it as “one of the world’s most unique festivals”, organisers said it was not sustainable.
Over the years, it has welcomed stars including Noel Gallagher, Pet Shop Boys and Mark Ronson, as well as Welsh singers, artists and writers.
Various organisations and magazines have given it awards, including title of best new festival in 2012, best small festival (2013 and 2015) and best line-up (2014).
It has also gained headlines for the wrong reasons, with hundreds of people left stranded after heavy downpours flooded a park-and-ride facility in 2016.
Organisers later defended the decision to place cars on a known flood plain, with some vehicles stuck there for days.
Describing the decision to put it on hold after 2018, they said it was “more than just a music and arts festival”.
“In six short years, the profile of the festival has far outgrown its intimate capacity, picking up numerous awards, gaining international recognition and becoming one of the world’s most unique festivals,” organisers said in a statement.
“We always knew we had something special but we never quite expected it to capture people’s imagination the way it has.
“Unfortunately, No.6 is just not sustainable in its current format and so we’ve made the difficult decision to take a breather – 2018 will be the last Festival No.6 for now.”
However, it added: “Taking a break is the right decision but not all is lost, we’re already thinking about the future.”
For this year’s event, park and ride facilities are at Llwyn Mafon Uchaf, Criccieth, which is outside Porthmadog and off the A487.
To deal with the the volume of traffic, diversions will be in place on a stretch of the road between Criccieth and Penrhyndeudraeth, with access for residents only.
The A497 between Porthmadog and near Minffordd station will also be closed to vehicles from 22:00 BST to 04:00 each night, while there will be a shuttle bus from Bangor station to the site.