Streymoy Island, The Faroes

Streymoy (Danish: Strømø) is the largest and most populated island of the Faroe Islands. The name means "island of currents."

Navigatio Brendani 11.2:

vīdērunt aliam īnsulam, prope sibi iūnctam, interveniente fretō nōn magnō. 

The "other island" is perhaps Streymoy, separated from Vágar by only a narrow strait.