WOW Airlines has a sale running right now featuring cheap flights to Europe from cities all over the United States. The cheapest treks you'll find are from Boston or Pittsburgh to Reykjavik, Iceland. You can get one-way flights for just $99 on that route and round-trip tickets for $199.98.
Other deals highlighted in the sale include cheap flights out of Los Angeles to Reykjavik ($129.99), London ($169.99), Copenhagen ($169.99), and Stockholm ($169.99). There are also deals out of San Francisco to Reykjavik ($135.99), London ($177.99), Copenhagen ($177.99), and Stockholm ($177.99). If you're in Boston or Pittsburgh, you can make your way to London, Paris, Amsterdam or Frankfurt for $149.99 one-way. All of those routes include a layover in Iceland, which can be a very good thing.