If you liked The Da Vinci Code, you can take a two-hour self-guided tour of Paris through the main places described in the novel (http://www.gpsmycity.com/tours/the-da-vinci-code-walk-in-paris-1414.html) or a four-hour guided tour (http://www.paris-tours-guides.com/gb/fr_da-vinci-code-paris.htm).
If you want to focus just on the Louvre, try this tour where a “symbologist” lets you revisit Robert Langdon’s around the Musée du Louvre. This tour (https://parismuse.com/tours/cracking-the-da-vinci-code-at-the-louvre/) begins and ends where his fictional caper does.
If you want to visit the locations featured in the London leg of Dan Brown’s novel, there’s a tour for that too: https://britmovietours.com/bookings/the-da-vinci-code-london-tour/.
And if you’re a real aficionado of the book and film, check out The Da Vinci Code Trail, a nine-day tour: http://www.operationeurope.co.uk/special-interest-groups/29-the-da-vinci-code-trail.html.
If Angels and Demons is your favourite, you can choose between a self-guided tour of Rome (http://www.italylogue.com/featured-articles/a-self-guided-angels-demons-tour-of-rome.html) or a four-hour guided tour (http://www.angelsanddemons.it/).
The third book in the Robert Langdon series is The Lost Symbol. It is set in Washington so why not do a self-guided tour featuring the landmarks from that novel: http://www.offbeattravel.com/washington-dc-lost-symbol-dan-brown-tour.html.
The latest book in the series is Inferno. It begins in Florence, and there are several tours from which to choose. You can do a two-hour tour (http://www.florence-museum.com/inferno-guided-tour-dan-brown.php), a half-day one (https://www.viator.com/tours/Florence/Dan-Brown-Inferno-Tour-of-Florence/d519-5049INFERNO), or a full-day walking tour (http://www.florenceinferno.com/walking-tours/inferno/).
There’s a Venice segment in the novel and of course there is a tour for that as well: http://www.tourleadervenice.com/project/inferno-dan-brown-tour-in-venice/.
Naturally, there are tours of Istanbul as well: https://www.viator.com/tours/Istanbul/Dan-Brown-Inferno-Tour-of-Istanbul/d585-8249P12 and https://www.lonelyplanet.com/turkey/activities/dan-brown-inferno-tour-of-istanbul/a/pa-act/v-8249P12/360857.
The fifth book in the series, Origin, will be released this fall. Who knows where it will take you.