Members of the Brecon Beacons Park Society are being shown how a gas pipe will be buried under the park - an area of outstanding natural beauty.
The park is a designated area of Outstanding Natural Beauty
The society had opposed running the 190 mile (320km) pipe, transporting gas from Milford Haven to Gloucestershire, across the national park.
But it now accepts it cannot stop the project and will visit a construction site to see how the pipe is concealed.
On Thursday National Grid won the right to evict protesters from a nearby site.
The High Court judge in Cardiff granted it immediate possession of the occupied land in the woods near Sennybridge.
The controversial pipeline is part of a project that will see liquefied natural gas (LNG) shipped to Milford from the Far East and converted to natural gas at two terminals at the port before being piped to join the National Grid's main network.
When complete, the pipeline will run from Milford Haven to Gloucestershire and eventually supply up to 20% of the UK's gas needs.
The £840m scheme has faced opposition including the Sennybridge tree protests and demonstrations at a site in the Swansea Valley.
Nigel Phillips, chairman of the Brecon Beacons Park Society (BBPS) said the society had originally opposed the passage of the pipe through the park.
But he said the society realised it could not stop the project and had decided to work with National Grid - which operates the UK's energy infrastructure - to try to minimise any potential damage to the area.
Mr Phillips said: "The Brecon Beacons Park Society has been vociferously opposed to such a large infrastructure project crossing an area with such important ecological and archaeological features.
Campaigners said their action was non-violent and peaceful
"At the same time we have realised that we would be unable to stop this project and so, have worked closely with National Grid to try and minimise the damage and monitor the inevitable long-lasting aftermath."
Following a presentation by National Grid and its contractors on Saturday, members of the society will be taken to a pipeline site to observe the construction process.
They will also be shown plans for the reinstatement and regeneration of a mountain common.
In the past, Brecon Beacons National Park Authority has also expressed concern about the project's effect on the environment, and said it did not believe the chosen route was the right one for the pipeline.
But National Grid said it regarded the environment as paramount and the most suitable route had been chosen after months of consultation.