All those that we visited (be it humble or seemingly luxurious restaurants) offered "tatami" experience and served grated wasabi as well as surprisingly amazing fresh sushi-sashimi platter at such a friendly price!
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Some places worth mentioning;
Kunti 2 : Jl. Bene Sari No 4, Kuta
Kokoya : Jl. Danau Tamblingan No 178, Sanur
Ryoshi : Jl. Hanoman No 68, Ubud