Good idea to rent bicycle
Good idea! Walking is good but renting a cycle in Seville is even better for the flexibility. All visitors can rent bikes. The popular services are Sevici and Centerbici. Almost the whole center of Seville has a bicycle lane, so there would not be much problem to go around comfortably and safely. Here is a map to consult the bike path:
How to rent a bicycle in Seville
There are several ways of renting bicycles in Seville, I can talk about the main ones "Centerbici" and "Sevici".
In Centerbici there are different rates: 3 hours - 8 euros, 6 hours - 10 euros, 1 day - 12 euros, each extra day 7 euros. You can also add some accessories such as helmets (2 euros per helmet), children's seat (5 euros) or reflective vest (1 euro). There is also a rental pack for two days with a price of 19 euros.
Sevici is very economical since it is part of the City of Seville. It works by bonuses and the first 30 minutes are free. The first hour would be 1.03 euros and from the second hour 2.04 euros.
Where to rent
For Sevici, you can rent at any terminal with a credit card. For a long-term subscription you have to register at the official Sevici website.
For Centerbici you can rent here.
You can rent bikes for up to 7 days as a tourist in Seville. The deposit is 150 euros and this is held on your credit card to be released when you return the bike in good condition.
Renting bicycle for the family
Electric bikes and child-friendly bikes are available by Sevici and Centerbici so there is no problem if you are traveling as a family. Though electric bikes are expensive at 10 euros an hour.
You can visit most of Seville on a bike as it is the 14th most bike-friendly city according to the 2017 Copenhagenize Index, and it's because the city's bicycle lane's infrastructure is made of over 100 km, everything you need to see in the downtown is near. Seville is a flat plain city, meaning no ups-and-downs that can make biking uncomfortable.
And the weather is (almost always) good.
You can rent electric bikes in Elecmove (in Calle Castelar) and another good bike rent place is Bici Activa (in Calle Asunción) but there are plenty in the city and they're not really expensive.
Sevici is the bike sharing system of the city and you can use the 7-day subscription service. You can get it in any Sevici station and you only need your credit card, it costs 13 € and the first 30 minutes are free each time you pick up a bike, so as a little trick, you can change bike every 25 minutes (there are Sevici stops in lots of places and if there are no bike slots available they give you 15 extra minutes to find another stop). They’ll withhold 150€ in your bank account as a deposit. When the weekly subscription expires, they will remove the withholding.