Two of the London bombers went whitewater rafting together in Snowdonia a month before they carried out the attacks, it has emerged.
Tanweer and Khan were also captured on airport cameras in Pakistan in February
Mohammad Sidique Khan, 30, and Shehzad Tanweer, 22, rode the rapids at Canolfan Tryweryn, the National Whitewater Centre, at Bala on 4 June.
Khan and Tanweer, from Beeston, Leeds, were photographed on the activity trip.
Police have confirmed the pair and two other men carried out the attacks in which they and 52 commuters died.
Khan's bomb, detonated at Edgware Road on the London Underground, killed six people while seven died at the bomb exploded at Aldgate by Tanweer.
The other bombs, at Kings Cross and on the bus at Tavistock Square, were set off by Habib Hussain, 18, also from Leeds, and Germaine Lindsay, 19, from Aylesbury.
Canolfan Tryweryn disclosed on Thursday that the two bombers had visited the centre a month before.
"Following liaison with the police, we are now able to confirm that customers with the names Sidique Khan and Shehzad Tanweer took part in a whitewater rafting trip on June 4," said a spokesman.
The pair, who are also known to have visited Pakistan together last November - Tanweer to attend Islamic training schools.
In the photo of the whitewater rafting trip, which they undertook with four other men, Khan is seen raising a two-fingered peace sign while Tanweer is leaning forward and appearing to laugh.
One of their friends gives a thumbs-up sign and another a wide-grin for the camera.
The four bombers seen on CCTV as they entered Luton railway station
It is believed both Khan, who was a teaching assistant at a Leeds school, and Tanweer, a sports science graduate, organised outdoor adventure trips for young Muslims from the city.
The Bala centre is the UK's leading national centre for recreational canoeing and rafting and attracts 80,000 visitors each year.
Last August Deputy Prime Minister John Prescott, on a short break at the centre, was involved in the rescue of a kayaker who got into difficulties at the centre.
The owner of JJ Canoeing and Rafting Centre in Llangollen in Denbighshire said he had passed on details to police of a group of four Asian men who took part in a rafting trip there in May.
Jim Jayes would not give the names of the men but said at least one was from the Beeston area of Leeds, where both Khan and Tanweer came from.