[hcrisp]

It appears to be a combination of "The Coming of Tuor to Gondolin" found in "Unfinished Tales" and "The Fall of Gondolin" found in "The Book of Lost Tales 2" [1]. The first covers Tuor's journey from Dor-Lomin to Gondolin in detail but stops there (Christopher Tolkien called it "one of the saddest facts in the whole history of incompletion"). The second covers the fall of the city itself in great detail. I read the two in that order recently and enjoyed the account immensely; it's on the order of Lord of the Rings in terms of a compelling story, grandeur and beauty.

[1] https://www.tolkiensociety.org/2018/04/the-fall-of-gondolin-...