In my home-spun campaign, players are about to discover the ruins of an ancient city. Long ago, there was a civilization with an advanced level of technology, which is now dead. I'm thinking of pitting them against the remnants of this civilization: their automated traps, fail-safes, etc. and perhaps some of them really survived 😉
What are some examples of "high-technology" traps and monsters in the D&D universe? I'm thinking clockwork/steampunk/magictech flavor. I was looking in the monster manual of 4.0, and found few creatures that fit this description. Golems maybe, and a couple of automatons. I was thinking of "hand writing" a few basic monsters by just changing the flavor of their attacks, but I'd prefer if there was some existing lore I could use.
Best Answer
Take a look at the Eberron Campaign Setting
Eberron explores the corollary of Clarke's third law (any sufficiently advanced technology is indistinguishable from magic) - that is to say it asserts that sufficiently advanced magic is indistinguishable from technology. It has a rich story that you can repurpose large swaths of.
Reflavor things, simply
A Whirling Blade Swarm is already a thing, but it's up to you how it came to be, and what drives it. Need a mechanical spider? Use a spider, and add the word "Mechanical" to its name.
Utilize Warforged
The Warforged are an Eberron player race that are, essentially, sentient robots. There's a wonderful backstory for how they came to be, but that's all you need to know if all you care about is the technological aspect.
There are 17 natively Warforged NPCs listed in the DDI compendium, ranging from minion to elite and levels 4-19.