This is part of the Dungeon of Terror, a massive underground complex from the mapping genius that is 0one Games. If you plan on using all of it, pick up their Dungeon of Terror Virtual Boxed Set, but this, like most of the sections, will work as stand-alone dungeons or as part of a complex of your own devising.
In the Dungeon of Terror, this section runs down the north-west - a complete map is provided so that you can see where it goes. It consists of some 25 rooms, and has a backstory to go with it, although you do need to populate it with monsters/NPCs and decide on room descriptions. The Dungeon was originally a dwarf mine which subsequently fell into the hands of an insane mage, who took up residence there. For a long time, nobody who visited emerged again, and there were many tales about the evil things the mage was doing... until he vanished. Some say an assassin finally got him, others that he's become a lich and is still around. Be that as it may, others have now taken over various parts of the complex, and the portion dealt with here was claimed by a brotherhood of assassins, led by an evil fellow who claims to be the reincarnation of the assassin who killed the mad mage. Or of course, if you prefer you can substitute your own backstory and inhabitants.
Whatever, whoever, you put in there, it is a well-provided lair for some group - maybe even your player-characters will take it over for a base once they have cleaned it out! The entrace is defended with a portcullis, but there are plenty of facilities for those who are allowed in, including a banqueting chamber, a shrine, bedrooms, a kitchen and plenty of storage - even a nice latrine with seat, washbasin and a curtain to let you have some privacy! One section, called the Chamber of the Test, is rather inconveniently placed between the sleeping quarters and the banqueting hall, so you need to remember how to navigate it when you want your dinner. The resident assassins being a nasty bunch, there's also a gaol and a large torture chamber - but from the looks of it, most of the more unpleasant equipment is portable if you'd rather use it for something else.
And that of course is possible due to the mastery of PDF technology we've become accustomed to from 0one Games. Using switches on the main plan, you can choose whither to have a hex grid or a square one (or none at all), if you want furniture or doors or a solid black fill to walls and the like. You can also use the plan to select which tile to print or to look at, empowering quite a lot of versatility as you decide just what you want to lay out in front of your players.
A useful item for your collection, a lair to invade - or perhaps to escape from, if characters are unlucky enough to get captured by the assassins - can always come in handy! And as ever, just looking at it spawns ideas...
Dungeon of Terror #2: Assassins' Brotherhood