Currently, only four EU/Schengen countries require Indian passport holders to obtain a Transit Schengen Visa in order to transit their territory, and these are France, Germany, Spain and the Czech Republic. Indian nationals can, however, transit through other Schengen Area countries, including here in the Netherlands.
Spain is a party to the Schengen Agreement. This means that U.S. citizens may enter Spain for up to 90 days for tourism or business without a visa. Your passport should be valid for at least three months beyond the period of stay.