When an internationally-known art museum undergoes a major expansion, it’s newsworthy. But it’s far more remarkable when two museums, each adding multi-million dollar expansions, are neighbors located less than a third of a mile apart. Such is the case with the Museum of Fine Arts and the Isabella Stewart Gardner Museum, both located in the Fenway section of Boston.

With over 450,000 works of art and the largest collection of Japanese works under one roof outside of Japan, the Museum of Fine Arts is a world-class institution. It has everything one would expect to find, such as outstanding examples of Egyptian artifacts, French impressionist paintings, and more. But when I come here with out-of-town guests, our tour always focuses on the early American art of guys like John Singleton Copley, Winslow Homer, John Singer Sargent, and Gilbert Stuart. In this area, nothing in London or at the Louvre eclipses the breathtaking examples to be seen here.

Playing to this strength, the MFA is adding a new wing devoted to Art of the Americas, a category that includes not only exhibits from the United States, but works from throughout North, Central, and South America. Designed by the firm of Foster + Partners (the architects of London’s City Hall), the wing will add 133,500 square feet of space and will increase the size of the MFA’s palatial Huntington Avenue location by 28%.

The wing, which by itself is larger than many museums around the world, will allow the MFA to display an addition 5,000 pieces of art. It also includes a studio arts classroom, “behind-the-scenes” galleries, and a 150-seat auditorium for films, concerts, and lectures. Surprisingly, this wing is merely the centerpiece of a renovation and expansion project which also includes a new visitor center (with “concierge” computers), two new conservation labs, a 8,280 square foot Special Exhibitions Gallery, and a 12,184 square feet courtyard and sculpture garden with a glass roof to keep out even the most inclement New England weather.

To fund all this, the MFA raised a dizzying $504 million in private donations, $345 million of which has been sunk into the project at hand. The remainder targeted for annual operations, the endowment of programs, and so on.

A stone’s throw away, the Isabella Stewart Gardner Museum has a far different character. It’s intimate and idiosyncratic, but that’s what makes it equally beloved. The building resembles a Venetian palazzo, and it does incorporate architectural fragments some very old European buildings, but the notion that the whole structure was shipped piece-by-piece from Europe is an urban legend. Regardless, to step inside is to step into another place and time, even if one could theoretically open a window and hear the not-too-distant roar of fans at Fenway Park.

“Mrs. Jack”, the art collector and bon vivant for whom the place is named, built this place as her home and filled it with things she considered beautiful. As you might guess, she didn’t shop at her era’s equivalent of Crate & Barrel. Instead, this place is filled with the works of major artists including Botticelli, Matisse, Titian, Vermeer, Whistler, and even Rembrandt. Sadly, this place has thirteen less works of art than it should because of a still-unsolved 1990 robbery in which two crooks disguised as Boston cops netted $500 million worth of goods. Called “the largest art heist in history,” the positive side of this bad event was that it turned world attention to the astonishing collection that remains here to be enjoyed.

Isabella, who left the place to the public with the stipulation that anyone named “Isabella” should be admitted free of charge for perpetuity, also stipulated that the place remain forever uncharged. But in 2009, the Massachusetts Supreme Judicial Court approved a deviation from the will to allow expansion.

The result will be a greenhouse-like addition that’s a thematic tie-in with the museum’s distinctive glass-covered court yard. The 70,000 square foot addition, designed by the firm of Pritzker Prize-winning architect Renzo Piano, will triple exhibition space. The $118 million expansion also includes classroom studios, conservation labs, apartments for artists-in-residence, and a multi-level performance hall designed with the help of renowned acoustician Yasuhisa Toyota.

By providing new space for offices and programs now cramped into the original structure, this new wing will make a good place even better. It’s scheduled to open in early 2012.

Some might wince at these multi-million dollar tags and say this money should be better spent elsewhere. While these may be well-meaning sentiments, this isn’t taxpayer money, and the combined cost of these expansions is less than (for example) one day waging war in Iraq. In return, we, the public, are getting spaces that can entertain us, educate us, and inspire us for generations to come.