Here's one of my favorite archaeologically documented oral legends.

The site of Chavin de Huantar was the center of a first millenium BC religious cult that spread its cultural influence across the entire Andes. Folks have been excavating there for decades now. The current team was excavating some areas just outside the main temple complex, looking for some residential structures. There they came upon a peculiar find. The skeleton of a middle-aged woman was found buried, stretched-out and arms crossed in the Christian fashion , with the remains of a few young children laid around her. Next to them, there were a number of young adult males, likewise positioned as modern burials. The town's cemetery, where other modern burials would have been placed, was not nearby. They were able to identify the men as Chilean soldiers by the metal buttons that had not corroded. You don't just find this anywhere. A local worker then told them a story, that other locals did verify as town legend.

From 1879-1883, Peru and Bolivia fought Chile in the War of the Pacific. Chile occupied Lima in 1881, and began to march their army north through the Andes to collect their loot. In Chavin de Huantar, locals talked of a local innkeeper who was approached for lodging by a small group of Chilean soldiers , scouting away from the main army. Not wanting to expose her town to their potential pillaging, she offered to house and feed them. However, she also planned to poison their drinks and discretely dispose of their bodies, so they would not be found by any future Chileans. The soldiers, though, expected her to drink with them. She resolved to die for her town, and had her children drink as well. Thus she died a hero and the town buried her and the soldiers outside the city limits.

I don't know if this qualifies, and I don't mean to offend anyone by calling it myths or legends - I just find the story interesting.

Many religions or societies have talk of a great flood, the most famous of course being the tale of Noah's ark. Such stories, find in a wide range of culture, seem to be based on a giant flood that actually did happen - http://www.theguardian.com/science/2000/sep/14/internationalnews.archaeology

In 2003 the fossil remains of a diminutive early hominoid called Homo floresienses were found on the Indonesian island of Flores and dated to as recently as 17k years ago. There has been plenty of debate regarding its speciation, that while interesting is besides the point. Anyways, an anthropologist from Canada who had extensive interaction with locals in the region in the preceding decades had recorded that multiple local traditions had reported interaction with a "short, hairy, humanoid" by earlier ancestors in the area. Some told of ancestors killing them, others that they still existed in the remote mountainous areas.

While they likely no longer exist, the fact that they're described by fairly recent stories (some stories were as recent as 200yrs old) proves interesting.

Andrea Carandini thinks not only was Romulus a real guy (at least in some sense), but he built the walls and temples and stuff he's supposed to have, and that he has archaeological remains. Six things specifically: the walls, three domi regiae, a house of the Vestals, an aedes Larum. Here is a BMCR review of his book.

Seems like a stretch to me.

The Trojan War . Popularly believed to be either a total fabrication or at least an amalgam of local histories and myths passed through oral tradition until in the 1860s, archaelogists discovered an ancient city pretty much where it was supposed to be, and proof that the city was destroyed by a great fire rougly close to the age the poems describe. It is believed this is city and its fate is what inspired the Trojan war tradition.