September 1, 1923 was a horrible day in Tokyo's history. Just before noon, a massive earthquake struck the area and destroyed many of the buildings. And like the 1906 San Francisco earthquake, fires ravaged the remaining buildings, driving people from their homes to find any open spaces they could find.
One of those spaces was a small block that formerly held the Army Clothing Depot. Tens of thousands took shelter here after the earthquake, but a firestorm killed 38,000 in this small block alone! As such, it was chosen as the site of a memorial to the victims of the quake - almost 100,000 in all.
The museum has a nice collection of materials, but certainly feels dusty and old. Children wouldn't be interested as there isn't anything to do; older children might enjoy looking at the models seen above. While it doesn't have the new, clean feel many museums have, it holds an important part of Tokyo's history. Admission is free, and a visit could be a quick addition before or after a visit to the Edo Tokyo Museum and Sumo Wrestling Stadium and Museum nearby.
The memorial and museum are located in Yokoamicho Park, reached by a short walk from JR Ryogoku Station. Use the exit for the sumo stadium, and make a right. Follow the road, with the sumo stadium on your right, for two full blocks. Make a right at that light (the hospital should be on your left after you turn), and you should soon be able to see the pagoda. If you arrive at Ryogoku Station via the subway, just head north down the main street (away from the elevated JR tracks) a couple blocks to the park. Free admission, open generally 9:00-4:30 except Mondays.