Wherever you are headed, the country's national parks list is the best starting point; parks get that status because they protect the landscapes the country itself considers its finest, whether mountains, lakes, coastlines, or forests. The official tourism board site and park service pages will show you the headline natural attractions quickly.
A few hard-won tips apply everywhere. The most photographed spot is often crowded to the point of losing its magic, while an equally beautiful alternative sits an hour away nearly empty, so ask locals for the second-best version of the famous view. Seasons change everything: waterfalls that thunder in the wet season trickle in the dry, alpine areas may be inaccessible half the year, and autumn or spring often beat peak summer for both light and crowds.
Check access practicalities before committing, since some natural highlights need permits, guides, four-wheel drive, or serious hiking, while others have cable cars and boardwalks. Start early in the day; nature at dawn is a different experience entirely.