AirHint found the following cheapest return flights from Seattle (SEA) to Keflavik (KEF) in September 2026 (see full year).
Return flights
| 30 Sep - 12 Oct | Icelandair | direct | |
| 01 Sep - 06 Sep | Icelandair | direct | |
| 04 Sep - 08 Sep | Icelandair | direct | |
| 13 Sep - 26 Sep | KLM | ||
| 20 Sep - 27 Sep | Icelandair | direct | |
| 13 Sep - 26 Sep | Icelandair | direct |
Also check the deals for one-way flights from Seattle to Keflavik in September.
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