Tā huàn xiǎng zìjǐ yǒu yī tiān néng huányóu shìjiè.
She fantasizes about traveling around the world someday.
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幻想 can be neutral (childhood fantasies) or slightly negative (unrealistic illusions). 科幻 (kēhuàn) = science fiction (abbreviation of 科学幻想). Compare: 梦想 (dream/aspiration, more positive), 妄想 (delusion, more negative).