In my mind, this is the real gem of the many undeveloped (or unmaintained) walls that dot the Mount Ann area. At the very least, it is the the tallest (30'-35') and widest (25'-30') of the little walls. At the same time, it presents several barriers to development. There is no possibility for natural protection and setting up a top rope is difficult. In addition, the rock is steep and barely featured. Oh, it very very tricky to find, and the bottom is slightly treed-in. But, hey, how many new areas are there on Cape Ann?!
In my mind, there at least two lines here, both hard. One up the left arete and another and the other a thin, slabby traverse starting from the left side and crossing over to the right side and up on slightly more featured rock. This looks like at least stout 5.11 and due to its length might be a true classic Cape Ann slab line (if such things exist).
Findiing it might be the crux. This wall is located above a swamp roughly between the main area of Redrock and the pipeline. Follow the path past Main Wall trending left. You will reach an depression with higher rocks in the woods around you. Sometimes there is a fire ring here. Head right up to an open area of rock. Lost Wall is off the backside of this over the swampy area.