Halcyon Lake is a lake of the Bjoulsae River that appears in The Elder Scrolls Online, located at the northern part of Bangkorai. It is the site of an Ayleid ruin known as Bisnensel (Ayleidoon: New Water Halls), or alternatively, Bisnensel-by-the-Lake.
The Ayleid city of Bisnensel was founded by King Laloriaran Dynar sometime between 1E 375 and 452, after having to flee Nenalata due to an ultimatum by the Alessian Emperor. The city prospered, however, between 1E 453 and 460, a priest of Hermaeus Mora known as High Priest Uluscant, established a congregation to this Daedric Prince, known as the Primeval Seekers. It attracted a considerable amount of the city's citizens, and as a result Uluscant's followers requested their leader be given more of a say in municipal matters.
King Dynar, a devout follower of Meridia, denied this request, refusing to share the leadership of Bisnensel with a group of scholars. Within a few months of his rebuff, Dynar was deposed as the ruler of Bisnensel, with he and his family fleeing to the Direnni Clan on the Isle of Balfiera. Uluscant then became the leader of Bisnensel, though the city later fell into ruin at an unknown time.