The old town was built around a strange and ancient tower of unknown origins. A man, trapped inside it since the dawn of time, can see and hear, but not interfere with, everything that happens around it.
Notice where the last comma is placed. You could remove but not interfere with, and the rest of the sentence would still make sense (although the meaning would be changed somewhat). With the comma in its original position, deleting the part set off by commas would give you […] can see and hear with everything that happens around it. Obviously, with belongs inside the commas.
Also, dawn of time doesn’t need to be capitalized because it’s a general concept rather than an actual, specific era.