Google Places API
Information about 100 million places

REST Countries
Information such as capital, currency and population per country

timezonedb
Time zone information based on the location

Numbeo.com API
Crowdsourced database with details about the cost of living, perceived safety and other topics for cities and countries worldwide

OpenWeatherMap API
Well, pretty obvious, right? Free tier!

Sunset and sunrise times API
Sunrise and sunset times – plain, simple and free

webcams.travel API
Access more than 50.000 outdoor webcams

izi.TRAVEL API
Provides access to a large collection of city and museum multimedia guides

RoadGoat API

RoadGoats Cities API provides content about towns, cities, regions, and countries (neighbourhoods coming soon). Content includes hand-picked high-quality photos, known-for tags (such as foodie or LGBT-friendly), editorial descriptions, Covid stats, safety rating, budgetary rating, and more.