After Oshamambe there's Uchiu Tunnel (内浦トンネル), Konbu Tunnel (昆布トンネル), Miyada Tunnel (宮田トンネル) and Niseko Tunnel (ニセコトンネル)
@matrix Why are you interested in this in particular?
@Mr_NutterButter I watched an Abroad In Japan video riding the shinkansen, checked the stops on Google Maps, decided to scroll the entire line and noticed there's construction in progress
Yoichi Tunnel (余市トンネル), after Kutchan Nitsuki Tunnel (二ツ森トンネル) and Shioya Tunnel (後志トンネル)