General Antonyms:
* Interior - This refers to the inner part of something, as opposed to the outward appearance.
* Reality - This emphasizes the contrast between the superficial and the genuine.
* Truth - This implies a lack of deception or pretense.
* Authenticity - This suggests genuineness and lack of artificiality.
More specific antonyms:
* Substance - If you're talking about a facade hiding a lack of depth, this could be an antonym.
* Core - This refers to the essential or fundamental part of something.
* Heart - This emphasizes the genuine feelings or nature behind an outward appearance.
The best antonym depends on the specific meaning you want to convey.