I am biased as I am Swiss and come from Geneva......We love to go to Zermatt in the summer. Magnificent walks, amazing matterhorn.....great temperature, Zurich and Geneva can get very hot in August and a lot of places don't have ac!!!September is often rainy.....My mum has apartments she rents all year round in Zermatt if you need more info. Gruyere is a lovely place to visit, obviously it has a cheese factory and a small town and a castle, great day out if you are in the area. Cailler have a great chocolate factory but it was a bit touristy and crowded last summer....chocolate was fabulous though!!!
