Yes, you will need a tourist visa to participate in the Annapurna Base Camp Trek guided adventure in Nepal. The tourist visa is granted to foreign nationals visiting Nepal and is valid for a maximum of 150 days in a visa year. The fee for a single-entry tourist visa for 60 days is US $60, with an additional $50 for multiple-entry visas. Extensions for tourist visas can be obtained for a maximum of 150 days.