Unless you're doing math (and are willing to take first order logic as a priori true) you need to start with something. Learning about the world requires data, data requires identifying a data source, and identifying a data source requires knowing at least one thing about the world.
As foundations go, it's hard to see how you could go any deeper than "I am having an experience".
As foundations go, it's hard to see how you could go any deeper than "I am having an experience".