Himring is a hill in the northeast of Beleriand, on which was the fortress of Maedhros, eldest of the Sons of Fëanor. After the drowning of Beleriand at the end of the First Age, the peak of Himring remained above the waves, known as the isle of Himling.
The fortress on Himring was built when the Sons of Fëanor went east after Thingol became aware of the Kinslaying. It was the chief fortress of Maedhros, from which he guarded the northeastern border region that became known as the March of Maedhros.
It stood firm through the Dagor Bragollach, and many survivors from the surrounding regions, including Maedhros' brother Maglor, rallied there. It remained for centuries, until the Nirnaeth Arnoediad; it is not mentioned after that in the Silmarillion as published, but the impression given is that it was forsaken, as the sons of Fëanor would no longer have had the strength to man it, had they chosen to.
After the War of Wrath, the top of the hill was all that remained, as a small island off the northwest coast; on the original maps that accompany The Lord of the Rings, it is labelled Himling. It is one of several high points in Beleriand to survive as islands and the easiest to locate, as it appears on most maps of Third Age Middle-earth.