Illegal activities aside, I’m thrilled people are using the tried and true ‘moveable bookshelf-secret chamber’ shtick!  It’s a classic.  For a great demonstration video, allow Gene Wilder to walk you through the process in Young Frankenstein.

PUT ZEEE CANDLE BACK!

Traps are a basic necessity, and range from ordinary lethal traps and at least one death trap (a torturous and needlessly complex device that causes a slow death that the hero will get strapped into instead of just being shot in the head, thus allowing a chance to escape and make a comeback).

Pit traps and things that shoot out of walls are popular designs among the technologically impaired, while those more gifted in this area show more variety but also a considerable tendency towards using lasers.

Sharks with lasers attached to their heads are an especially effective deterrent to would-be do-gooders though they can also be hard on the hired help.
Other goodies

Other common furnishings include but are not limited to:

* A main control room with a great viewscreen and a digital countdown clock
* An inner sanctum that may double as a meeting place with other heads of the underworld
* Fiendish laboratories that are crawling with crimes against nature. If the villain has any inclinations towards biochemistry, monster/mutant cages that invariably prove too flimsy in a real emergency, or hero attack.
* A self destruct system-how stereotypically wonderful,really original.A self destruct swift seem like a terribly stupid idea from first glance,but this little red button can provide your much needed 30 seconds of escape time(it’s likely the most expensive 30 seconds, so make them count), or after your beaten, you wouldn’t want the police or a henchmen using your secret documents for themselves would you? Hell no, all your shit is coming with you .

Sentient and malevolent AIs are a bonus.

Secret Evil Lairs?

Secrecy is optional, but plots tend to revolve around the hero finding the lair as well as entering it. The job of the henchmen is then to engage the hero in single combat (when one good rush would finish him off) using their unique specialties, while the minions work feverishly on the final stage of the evil plan and die a lot.