Mr. Nussbaum Explorers is an interactive site with profiles of 22 explorers of the Americas. Other sections include: pirates, legends and myths, a summary of the Age of Exploration, Lewis and Clark, Marco Polo and the Silk Road, and an interactive scavenger hunt.
Sections with teacher resources include printables and reading comprehension multiple choice questions.
My observation is that some of the reading materials score at a higher grade level than what is recommended on the site. Also, you may encounter pop-up ads that block content until they are dismissed. The site has posted a notice that it is revamping layout and ads in 2018.