For Nigerien citizens planning a journey to Turkey, a visa is indeed a mandatory requirement, with several options available including work, tourist, student, and transit visas to suit your travel purpose. You can typically expect tourist visas to allow stays of up to 90 days, though this can vary based on the specific visa type and your individual circumstances. When planning your trip, remember that Istanbul's bustling markets are best explored outside the peak summer months of July and August to avoid the intense heat and crowds. Also, familiarize yourself with basic Turkish phrases, as while English is spoken in tourist areas, a little effort in Turkish can go a long way in enhancing your experience beyond the standard flight routes.