このやや珍しい形の岩は、まるで平たいつばつきの竹の笠が柱に載っているように見えます。伝説によると、高野山の開祖である空海が山を登っているとき、笠が風で飛んでここに着地したということです。
柱のてっぺん近くには、小さな阿弥陀如来の姿と柱が南北朝時代のものであることを示す銘が刻まれています。おそらくこの石柱は、もとは木でできていた柱を置き換えたものです。
笠石は三谷坂の主要な見どころのひとつです。

Kasa Ishi (Bamboo-Hat Rock)
This rather unusually shaped rock strongly resembles a flat-brimmed bamboo hat resting on top of a pillar. According to legend, when the priest Kukai (known posthumously as Kobo Daishi; 774835), the founder of Koyasan, was making his way up the mountain, the wind swept away his bamboo hat and it landed here.
Near the top of the pillar is a small carving of Amida Nyorai (the Buddha of Infinite Life and Light) and an inscription dating the pillar to the Nanbokucho period (13361392). The stone pillar was likely made to replace an original wooden version.
The Kasa Ishi is one of the major landmarks on the Mitanizaka Trail, which continues to the right at the nearby fork in the road.