Seville Self-Guided Audio Guide of the Historic Center
It is a real self-guided audio guide, not a generic app with text read by an artificial voice. The script is written and narrated by a local guide from Seville, with the same stories he would tell on a live tour. The audio activates only when arriving at each stop thanks to the GPS, and the app itself gives walking directions from point to point, so the traveler does not need to follow a separate map or guess where to go. There is no schedule or group: you can start any day, at any time, and repeat it as many times as you want during 30 days. It works live with data or downloaded via Wi-Fi to use it without coverage, something useful in historic castles where the signal fails. It is an app with audio guides from local guides in more than 20 cities, so whoever tries it once usually uses it again on their next trip.
Prices may vary slightly on the provider's site — you could get an extra discount at checkout.