Tuesdays only, solo diners welcome.
In Yotsuya Arakicho, there's a small bar called "Ba BAR" that quietly opens only on Tuesdays. It's a bar where you can drink "Ba," which stands for barium contrast agent (or something that looks exactly like it) used in X-rays. It's probably the only one of its kind in the world. It's basically open every week except on public holidays, so feel free to drop by.