User-generated content (UGC) has become one of the most influential sources of information affecting tourist decision-making in the digital age. Platforms such as TripAdvisor, Instagram, Facebook, YouTube, Google Reviews, and travel blogs provide authentic, experience-based insights that increasingly shape destination image, perceived value, trust, and intention to travel. This research investigates how UGC affects travel decisions by analyzing a multi-method dataset consisting of tourist surveys (N=580), content analysis of 1,000 online reviews, and interviews with 14 tourism professionals. Results show that UGC is perceived to be more credible and emotionally relatable than traditional marketing material, significantly impacting destination choice, accommodation selection, itinerary planning, and overall travel behaviour. Challenges include fake reviews, information overload, algorithmic biases, and reliability concerns. Recommendations are offered for tourism marketers, platform designers, and policy-makers.