There was plenty of hype in Washington last year when author Dan Brown released “The Lost Symbol,— his latest cryptology-laced thriller following the conspiracy-filled adventures of fictional Harvard University professor Robert Langdon.

And while much of the excitement surrounding the novel has subsided in D.C., the book continues to soar nationwide — it remains firmly planted on several best-seller lists, and Columbia Pictures already has announced the book will be turned into a movie. For those who are still obsessed with Brown’s novel, “An Illustrated Guide to The Lost Symbol— might just be the perfect companion book.

Brown’s novel follows Langdon as he spends 12 hours searching for the secrets of the fraternal organization of Freemasonry throughout the nation’s capital, from the Washington Monument to the Capitol to the Smithsonian Institution and other notable locales. In this unauthorized companion book, edited by John Weber, readers can learn the actual Masonic secrets behind each spot where Langdon stops, as well as get a basic history of Freemasonry.

For Washingtonians, and especially those who work on Capitol Hill, some of the secrets in the guide aren’t all that mind-blowing. There are clinical, textbook-like sections on the construction of the Capitol and Library of Congress, details that any lower-level staffer who has given a tour of the Capitol likely already knows.

But that’s not to say there isn’t some interesting, insider-type stuff in the book — and it makes a great gift for that out-of-town relative who loves Brown’s novel.

Organized into six chapters, the guide begins where Langdon begins, at the House of the Temple, 1733 16th St. NW. The ornate building serves as the headquarters of the Scottish Rite of Freemasonry, Southern Jurisdiction of the United States, and as the setting for — spoiler alert! — the climax of the novel.

While at first the House of the Temple appears cloaked in conspiracy — with its gold, unfinished pyramid roof and 33 columns (each 33 feet high) — the guide spills some of its secrets. Designed by architect John Russell Pope, who also drew up plans for the Jefferson Memorial and the National Archives, the House of the Temple is modeled after the Mausoleum at Halicarnassus, one of the original Seven Wonders of the World.

One of the highlights of the building is “The First Inauguration of George Washington, April 30, 1787,— a historic painting hanging in the George Washington Memorial Banquet Hall. The painting features the beloved president at his inauguration alongside several other Revolution-era figures, many of them Freemasons.

(In case you didn’t know, George Washington was a Freemason, and the fraternal organization is pretty proud of that.)

There’s also information on the temple’s massive sphinxes, located near the front door. One sphinx has its eyes open and the other’s are closed, which the guide argues is an allusion to engagement to the outside world while also taking time for contemplation.

The chapters on the Capitol and Library of Congress, meanwhile, aren’t too revealing — one could find most of this basic history on the Architect of the Capitol’s Web site. There also are essays about the Washington Monument and Smithsonian’s Museum Support Center, which, by the way, houses unique treasures such as the Smithsonian’s giant squid.

“An Illustrated Guide to The Lost Symbol— is in stores now.