Wow congratulations! Your choice for summer travel destinations are almost endless. First decide what you want to do ie sports, culture, history etc. Then decide between hot and cold weather and then city or beach. You could both also make a shortlist of 5 each secretly and compare your answers. There is a guide to every country in the world here http://www.puretravel.com/Guide broken down by continent then country. Also think about your budget and where will give you the best value for your money and then also how much time you can both take off. Hope you have a great time!!
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Well in my view I like Switzerland for summer, Well you can also search it by online by seeing every thing about different place like things to do, hotels, accommodation and etc. You can check here http://www.all-travelguide.com/