The Willow Marsh is the only place in the Eidolon map where willow trees can be found. It can be reached by following the path of the Transmission Towers towards Bellevue, and is specifically close the fallen tower in the lake pictured on the Transmission Towers page. The water is shallow with many small islands scattered about and there are hundreds of small stone ruins in both the water and on land. Several artefacts can be found here.

Willow Marsh 2
Willow Marsh 3
Willow Marsh 5
Willow Marsh 4
Willow Marsh 6
Willow Marsh 7