Zurich's annual Sechseläuten spring festival (a centuries-old guild celebration marking the end of winter) takes place on Monday 20 April, with thousands of visitors expected in the city centre. The centrepiece is the burning of the Böögg — a snowman effigy filled with firecrackers — atop a ten-metre bonfire at 6 p.m. on the Sechseläutenplatz, with folk tradition holding that the faster the Böögg's head explodes, the finer the coming summer will be. Weather forecasters are predicting a mix of sun and cloud with temperatures around 18°C, favourable conditions for a swift burn, while this year's guest canton Graubünden adds an alpine flavour to proceedings, including a special red Rhaetian Railway-liveried tram that will continue running through Zurich's streets in the months ahead.