A 'topping out' ceremony has been held on the construction site for The Castle leisure centre at Elephant & Castle.
The building has now reached its full height but it will take another year to complete the work.
When it opens in spring 2015 the new centre will include a 25-metre swimming pool.
"Seeing the progress today has been brilliant," said Cllr Peter John, leader of Southwark Council.
"We can't wait to see The Castle centre completed next spring, ready for our residents to use. Today's ceremony has been a great milestone in the journey to throwing open The Castle doors for the first time.
"The Castle is just one part of the exciting £3 billion transformation we are undertaking here in Elephant & Castle and it will be a great addition to the area and to our leisure facilities in the borough."
Neil Patterson of Balfour Beatty added: "We are delighted to have reached this significant milestone in the construction of The Castle leisure centre.
"Through close collaboration with Southwark Council we have designed a facility to fully meet the demand for improved leisure centre facilities in the area."
Addressing construction workers, Cllr John said: "This leisure centre is going to be one of the first symbols of the regeneration of the Elephant & Castle, so you've been involved in massively important project.
"Thank you on behalf of the people of the borough for the work you've been doing; it's really appreciated."