Zevachim 109 - Does One Need an Altar to Sacrifice Outside?
According to Rabbi Yose, one is not liable for offering up outside, unless he offers the sacrifice upon the top of an altar, but Rabbi Shimon says, "Even if he offered up on a rock or on a stone he is liable."
What is Rabbi Yose's reason? - It is written, " and Noah built an altar to God " - which proves that an altar is required. And what is the reason of Rabbi Shimon? - It is written, " And Manoach took the goat-kid and the flour offering and he offered them up on the rock to God. "
How does Rabbi Shimon explain Noah's altar? - He says it was built only to provide comfortable height upon which to perform the sacrifice. And how does Rabbi Yose explain the rock of Manoach? - An angel told Manoach to act thus.
For what sacrifices is one liable when offering them outside? - Any valid sacrifice, or even an invalid one if it would be accepted on the Altar after the fact. One is liable for offering an olive's volume of the meat, flour, and incense. For non-blood offerings, Rabbi Elazar makes him liable only for a complete amount.
Art: Adam Colonia - Noah Leaving the Ark