The important thing with Dan Brown novels is that one has to treat them them as historic fantasy stuff and then it's actually OK for a public transport read. I read Illuminati on a long train ride and was OK on being a, unintentionally funny, page turner thriller.
It's simply an action film in a book. To be more precise like the National Treasure movies featuring Nicolas Cage.
I think one of them involved breaking into the buckingham palace, the white house and then also kidnapping the US president within half an hour and also rubbing lemon juice on the back of the decleration of independence because of some invisible ink clue to find some hidden templar gold in the US.
Dan Brown's Illuminati features a hyper-speed jet(MACH 5+) and an antimatter bomb literally 10 pages in and also papacy by acclamation. Rigth from the start it obviously is scifi/fantasy.
I know a few people who studied history of arts or archeology and they love both (dan brown novels and nicolas cage's national treasure movies). Because it's pure comedy to them. They all also love Indiana Jones and Tomb Raider despite the obvious lack of professionalism in their work
One guy has a whole bookshelf to such mystery-history -fantasy novels which feature stuff like
-jesus artifacts,
-holy relics in all variants,
-murders in the vatican,
-grave robbing
-traps inside a secret temple
-inka amuletts with strange powers
-cursed digging sites, very likely deadly virus,
-unknown dangerous henchmen said hunting, relic,amulett, artifact or virus
-some conspiracy by a holy order
-all of the above
For him it's just like hacking scenes in movies are for me. Absolutly hilarious.
The problem is that a movie with such silly content is obviously pure fantasy/fiction because the viewers see actors doing things while in book form an awefull lot of people simply believe things because they are written.