#the talking purse; that one suspicious fox; basically everything in the old forest

[sesamenom]

I wonder what part of Rivendell's protection is Turgon/Gondolin-inspired, on top of the Bruinen basically acting as a proto-Girdle?

looking at the map, the actual valley is mostly enclosed by the Bruinen, with the Trollshaws on one side and the Misty Mountains on the other.

the Map of Wilderland gives a bit more detail in the region, particularly around Mirkwood/Beorn's house. from here, it looks like the Eyries were somewhere around the Misty Mountains a bit north of Rivendell:

for comparison, here's Gondolin and Doriath:

the FA-era eyries seem to mostly have been around the Crissaegrim/Cristhorn area enclosing Gondolin, while the Girdle followed the approximate shape of the rivers around Neldoreth and Region, and Lorien's Girdle seems to kick in at around the Nimrodel:

so it makes sense for a potential Girdle of Rivendell to lie around the Bruinen, especially given Elrond's apparent control over the river (despite having Vilya and not Nenya - maybe it's an Ulmo/Earendil's Star derived thing?)

I don't think we've explicitly seen anybody trying to get into Rivendell and just getting lost at the Ford, so it's probably more of a manual Girdle: it doesn't actually stop people from finding the river itself, but Elrond gets a mental notification or something and can flood the river to wash intruders away.

Beyond the Ford, it does definitely sound like the travel time to Rivendell varies. This (plus the varying road length/road time) can probably be attributed to the time warping effect of the Three, like a weaker but much larger version of Lorien's time related stuff.

so basically it seems like there's a combination of the Bruinen acting as both a manual Girdle, plus the time distortion between the Ford and Rivendell, as well as possibly hiding Imladris in a similar way to Ulmo hiding Gondolin?

A bit of a theory that I’ve struck on while rereading the start of FOTR. I think there’s something guarding Rivendell besides the Bruinen. I think Elrond has taken a leaf out of Melian’s book.

There are some hints that the distance to Rivendell varies depending on who you are. Frodo starts approaching the Ford in late afternoon; he is in desperate need of healing, and is brought to Rivendell midway into that same night.

In The Hobbit, in contrast, the dwarves and Bilbo cross the Ford of Bruinen in the morning, and the sun is down by the time they reach Rivendell. There’s lot of references to the journey being longer than Bilbo would expect:

They came on unexpected valleys, narrow with steep sides, that opened suddenly at their feet, and then looked down surprised to see trees below them and running water at the bottom. There were gullies that they could almost leap over, but very deep with waterfalls in them. There were dark ravines that one could neither jump over or climb into. There were bogs, some of them green pleasant places to look at, with flowers growing bright and tall; but a pony that walked there with a pack on its back would never have come out again. It was indeed a mich wider land from the ford to the mountains than you would ever have guessed. Bilbo was astonished.

Then there’s Aragorn’s line when Merry asks him how far it is to Rivendell:

“I don’t know if the Road has ever been measured in miles beyond The Forsaken Inn, a day’s journey east of Bree. Some say it is far, and others say otherwise. It is a strange road, and folk are glad to meet their journey’s end, whether the time is long or short. But I know how long it would take me on my own feet, with fair weather and no ill fortune: twelve days from here to the Ford of Bruinen.”

(By the way, it always amazes me, now I’ve noticed it, that the hobbits manage this journey - which Aragorn says would take him 12 days on the Road, with “fair weather and no ill fortune,” in only 14 days with Frodo severely injured, travelling mainly off the Road, and with some bad weather and wrong directions. Some of that’s due to the extremely fast pace Glorfindel sets for the last twoand a half days, but it’s incredibly impressive.)

If anyone should know the distance from Bree to Rivendell, it should be Aragorn, a Ranger of the North fostered in Rivendell, who has probably covered that journey dozens to hundreds of times. And the Road is fairly straight; it shouldn’t be hard for travellers to keep track of the general distance. And also, Aragorn only gives the distance to the Ford, not to Rivendell itself. What if the distance and difficulty of the Road from the Ford to Rivendell varies, based on how well a guest is known. Frodo is the Ring-bearer, in desperate need; he makes it there fast. Thorin & Company are vouched for by Gandalf, but are largely an unknown quantity; it takes them the better part of a day. Someone with hostile intentions might never find Rivendell at all, even after days of wanderings.