Best free "dungeon crawl" games

Dungeon crawling was the main player goal in the first CRPG (Computer Role-Playing Game) ever to came out on a computer. The first CRPGs were a sort of early roguelikes back then, and by "back then" I'm talking decades ago. Later, thanks to the capabilities of the PCs of the 90s, dungeon crawlers shifted to "half" of a 3D visual (it was 2D simulating 3D, actually) and became much more appealing to a much broader audience. That was when developers designed some of the greatest RPGs ever for PC:

• Dungeon Master - an instant classic, the one that started the 3D dungeon crawling mania
• Eye of the Beholder - the series that better represented the dungeon crawlers in the 90s
• Wizardry - something more than a mere dungeon crawler; a long time running series that lasted more than many other RPG franchises
• Might and Magic - like Wizardry, Might and Magic was something more open world-like, but managed to keep that dungeon crawling feeling

These games were perhaps the most popular of their time; many pages were written about them on every video game magazine of the 90s.
When Wolfenstein 3D (and Doom) shocked the gaming world with its real-time 3D environment, almost every CRPG developer started to look in a new first-person direction: no more turn-based movent, enter real-time (see Ultima Underworld). That meant a lot of changes and 3D/2D dungeon crawlers started to quickly lose their appeal.