Short answer
The Azores has many officially marked trails (trilhos) across the islands, but the 'best' depends on your fitness and the island. Popular regulated routes include trails around Sete Cidades and Furnas on São Miguel, and the Caldeira and Mistérios on other islands. Always check trail status and weather with the official Azores trails website or local tourist office before setting out.
General information, not legal or tax advice. Rules and amounts change: confirm with official sources.