It seems that so much is revealed by paying attention. Even in language, taking a close look at some common words uncovers a depth. Actually considering what it is to re-member, re-cognize, or real-ize is a fascinating exercise. It even works for words that don't begin with "r". For example, how illuminating to understand what it means to be mis-taken. Any aspect of manifestation - physical or mental - quickly swells, ripens under the eye of the mindful (that's you). We need only to take the time and train the mind in this capacity.
Advaita Vedanta is an ancient India philosphy. Shankara is its most well-known teacher, though it's really impossible to mark a "founder". It's far older and deeper than any one person.
We might expect something pretty alien in such a system of knowledge. Something silly, perhaps about Vishnu, Shiva, or Brahman and the birth of the world through the mouth of a turtle, or something. But this is to confuse mythology and philosophy. (There IS a prominent turtle in Indian mythology, but that's for another blog...) We need only some simple translation and etymology to bear the fruit of Advaita Vedanta.
A: not/dvaita: two (things) Veda: knowlege/anta: end of, culmination or pinnacle of
Advaita Vedanta: The culmination of knowledge is that there are not two things.
There is only one.