Drill hole through rock wall?
Diamond hole saws work well for this with water. If this is anything like the stone foundations I have worked with there will never be a straight mortar line that could be used. On one of the first walls I drilled through I used a hammer drill and bit , The hammer drill caused the rock to break out on the back side and it was very tough to repair. This is the type of drill. once I get about an inch in I chip out the center and go deeper repeating the chipping process as I get close to the bottom of the saw. A really Good quality one may make it depending on the rock type. Don't go cheap or you will spend more time getting new ones and even though they are close to the same size sometimes you ending up having a slightly larger bit the second time (also found this out the hard way)