Underground Kent has an excellent story on the Margate Lido. Visit the site for more information and photos. An extract below:
"In the 1920's the Lido at Cliftonville was completed to cater for the popularity of sea bathing. The Lido was built on the existing Clifton Baths Estate, beneath which ran many passageways used by smugglers in previous centuries. The underground complex consisted of bars, cafes and an indoor warm sea water pool with nearby changing facilities. The Lido was hugely popular from it's construction right through to the 1960's. A winter storm in January 1978 which destroyed Margate Pier also wreaked havoc with the Lido, particularly the outdoor pool. Reconstruction work was never even considered, and even today the Lido faces almost certain demolition."