According to Genesis, Noah built an altar after leaving Noah’s Ark.
Genesis 8:20 says that Noah built an altar to the Lord after the floodwaters had receded and he had come out of the Ark. He then took some animals and birds described as clean and offered burnt offerings on it.
The altar is presented as Noah’s first recorded act after the rescue. It expresses thanksgiving and worship, and the following verses describe God’s response and the continuation of the world’s natural cycles.
This episode is sometimes confused with the later covenant sign of the rainbow. The altar and the rainbow belong to the same post-flood sequence, but they are different events: Noah builds the altar, while God establishes the covenant and gives the rainbow as its sign. Genesis does not say that Noah built a temple or a permanent sanctuary at this point.