For a day in Reykjavik, a great plan includes visiting iconic spots, exploring museums, enjoying local food, and taking in the scenic views by the waterfront. Here is a suggested itinerary:

• Start your day early with a walk to the Sun Voyager, an iconic steel sculpture resembling a Viking long ship with beautiful waterfront views.
• Have breakfast at nearby Sandholt bakery/cafe, famous for its pastries and breakfast options.
• Visit Hallgrímskirkja Church, Reykjavik's iconic modernist church with a tower offering panoramic city views.
• Walk down through the city center to the Sun Voyager sculpture by the waterfront, a great spot for photos.
• For the afternoon, consider heading to the Perlan Museum with its interactive exhibitions on Iceland's nature, including an ice cave.
• Explore Reykjavik’s main shopping street, Laugavegur, and the nearby Rainbow Street, known for its colorful pavement and local shops.
• Visit one or two museums such as the Saga Museum, Reykjavik Maritime Museum, the Icelandic Phallological Museum for something quirky, or the Settlement Exhibition.
• End your day at Harpa Concert Hall to admire its unique glass architecture and light displays.
• If time and weather allow, consider a food tour or a relaxing stroll in Hljómskálagarðurinn park.

This plan covers cultural, historical, architectural, and culinary highlights of Reykjavik in a single day.