The case tunnel presented in the paper, located in coastal highway at eastern Taiwan, passes through Paliwan Formation and Fanshuliao Formation.  The rocks are mainly composed of conglomerate, sandstone, mudstone and their interlacing.  During route selection and planning stages, the geological properties, terrain characters and traffic maintenance have been considered, and the ecological and environmental protection, landscape and the construction technology are thoroughly examined.  However, the rocks suffer severe weakening as saturated, meanwhile the timedependent deformation are also distinct.  These unfavorable engineering characteristics resulted in the variation of landforms happened in evidence, and jeopardized tunnel construction many times.  This paper reviews the route selection and planning tasks of the tunnel, and lessons learned from the project are commented accordingly.