This is the 67th most frequent Romanian word.
alte
"Alte" means "other" or "different" in English, used for feminine plural nouns.
In this sentence, 'alte' is used as the plural feminine form of the demonstrative pronoun, indicating additional books different from the ones previously mentioned.
Am citit niște alte cărți interesante.
I read some other interesting books.
'Alte' here modifies 'teme', acting as an adjective to specify a different set of themes separate from the original ones.
Alege alte teme pentru proiectul tău.
Choose other themes for your project.
In this context, 'alte' describes 'clădiri' as additional or alternative buildings accessible for visiting.