Public transport is definitely an option to get to Reddings Retreat.

From Chepstow
You can either get a train or bus to Chepstow.
If you take the train to Chepstow station you will need to travel from the train station to the bus station (bus C1 or C3). It’s a 3 minutes journey and the buses run every 5 minutes. Then from the bus station it’s the 69 bus to Tintern and is a 16 minutes travel time to George bus stop opposite Tintern Abbey. Then either walk up the Wye Valley Footpath to Reddings Retreat or walk along the A466 out of Tintern towards Reddings Retreat. More detailedinstructions are provided with booking confirmation. 

Taxi from Chepstow to Reddings Retreat cost from £16 to £21 for the 14 mile journey. 

From Monmouth

You can take the 69 bus from Monmouth and it's a 24 minute journey to Tintern Abbey Bus stop. Then cross the road and walk up the Wye Valley Footpath to Reddings Retreat or walk along the pavement of A466 out of Tintern towards Reddings Retreat to the farm drive.
More detailed instructions are provided with booking confirmation. 

Taxi from Monmouth to Reddings Retreat, Tintern costs from £31 to £37 for the 21 mile journey. 

From Bristol Airport (BRS)

You will need to either take two buses to get to Chepstow, which will take just over 2 hours or a bus and a train which will take 2 hours 15 minutes. Then follow the directions above 'From Chepstow'.

Taxi from Bristol Airport to Reddings Retreat, Tintern costs from around £70 to £90 for the 27 mile journey.

From Cardiff Airport (CWL)

You will need to take two trains to get to Chepstow from Cardiff Airport, which will take 2 hours 30 minutes. Then follow the directions above 'From Chepstow'.

Taxi from Cardiff Airport to Reddings Retreat, Tintern costs from around £90 to £120 for the 44 mile journey.