The entry point to the Timeless River from Disney Castle, The Cornerstone of Light unguarded, Also of note on Cornerstone Hill are four Windows to the Past that eventually open as the story progresses; each of these leads to a new area based on a classic Disney short film. From left to right, the windows are:

The Building Site, a construction site with a rickety platform and based on the 1933 short Building a Building.
Lilliput, a tiny town with a big cannon that can be activated by jumping on it. It is from the 1934 short Gulliver Mickey.
The Scene of the Fire, a big building with fierce flames that was inspired by the 1930 short The Fire Fighters and the 1935 short Mickey's Fire Brigade.
Mickey's House, which shows the inside of Mickey's House, decorated for Christmas, a la the 1931 short Mickey's Orphans.