My wife and I both felt Balboa Park as a whole probably should be rated as the #1 attraction in San Diego. However, various parts of this huge park are reviewed and rated individually and separately such as the Globe Theater, the zoo, etc.
In past years we have visited the outstanding zoo as well as several of the museums (most have admission fees). But this most recent trip we focused on visiting the gardens and the Botanical Building (free) and most of their gardens (all free, except the Japanese Tea Garden). We especially liked the desert and rose gardens. We also liked the Spanish Village which featured a variety of artists. One gallery featured live glass blowing demonstrations which I found very interesting. All of this was free. We easily spent a couple of days enjoying this park.
One feature of this terrific park we would not recommend was the hike in the western strip of the park (north and south, west of the 163 highway that cuts through the park. This hike is fine if you mainly just want to take a long walk, but the "featured sites" along this hike were not very interesting.
The main visitors center for the park is very good, staff helpful and friendly.
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