Fenway Park is home to the Green Monster, but it’s the LEED-certified Nationals Stadium in Washington D.C. that is the true green monster.

As National Geographic’s Green Guide points out, the Washington Nationals aren’t the only sports team building green.

The new Yankee Stadium and Citi Field (New York Mets), on the other hand, passed on the option to build sustainable venues, even though they were able to spend $1.5 billion and $900 million respectively to build their new stadia.  The green upgrades in Nationals Park, by contrast, cost but $2 million.