How about the old Masaryk Ring then?
"The Masaryk Ring near Brno was the longest circuit used in Grand Prix racing in the 30's. The site of the Czech Grand Prix was named after their founding President Thomas Garrigue Masaryk. Half the circuit used the national highway and the other half was on local district roads. The local roads were narrow and very bumpy. Because of the length of the circuit crowd control was problematical. In 1937 Herman Lang lost control and crashed into a crowd of spectators who were standing in a prohibited area.
Length: 29.14 km (18.10 miles)
Fastest Lap: Caracciola (1937) - 11 min. 59.3 sec. 145.9 km/h (90.66 mph)"
http://www.grandprixhistory.org/track.htm