I spent a very hot weekend in Geneva recently and found the perfect cure to the heat - Les bains des Paquis is a city beach on the shores of Lac Leman. Entry is two CHF for unlimited time. In addition to the pebble beach and the lake, there is a restaurant (which serves an excellent salade Greque), a hammam with massage services and a games area.
Sounds tacky? I thought it would be, but it wasn't! Swimming in the lake in the height of the summer with city views all around, the jet d'eau in the background and the snow-capped mountains in the distance is really something else.
It's on the same side of Lac Leman as the Cornavin station. Walk down to the Quai Mont Blanc and head left (towards the parc mon repos), the bains des Paquis are clear signposted and are accessed via a bridge.
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