One of the hardest, but most rewarding parts of running a role-playing game is writing the game itself. Unless you are using a premade adventure, or a “module” as they are frequently called, the game master is responsible for creating a world, the people within it, and the problems that the players need to solve. That can be a lot to come up with on your own, but by borrowing ideas and content from history and freely available resources, a game master can save a lot of time and effort that could be better spent polishing ideas, instead of inventing them wholesale.
This resource contains a wealth of information on the history of myths from different cultures around the globe. Some of the best fantasy is rooted in real myths, and by using the structures and interesting details of mythology, a game master can craft resonant stories. Not every entry in the encyclopedia will be well fleshed out, but each entry contains links and references to quality source material. Use this resource to come up with ideas to flesh out on your own or with further research.
From The Lord of the Rings onwards, symbology has been a mainstay of the fantasy genre. Player’s love interesting symbols and runes, but doodling them from scratch can often come off as goofy. The Encyclopedia of Symbols contains a history of real shapes drawn or carved by real people, and the weight of this history can lend weight to a fictional world. The database does contain symbols that will probably not be useful, such as emojis, but the Graphical Index tool can be used to find the shape language that fits your game best. Once you find a symbol that you like, you can find other related symbols by browsing its category.
This blog contains hundreds of high quality, freely available maps created by Dyson Logos, a professional illustrator. The navigation tool on the lower right of the page contains links to archives of maps by subject, including dungeons, cities & towns, taverns, and more. A good map can bring a location to life by providing more details for players to delve into than a narrator could ever describe. For those running dungeon crawls, a subset of play focused on room-by-room exploration of dangerous spaces, these maps provide a strong basis to work from, as they contain looping designs that make moving through their spaces easy and expressive. Many of these resources are available with a license for play, but must be purchased if being used in marketing.