* Formal: "Spero che il suo soggiorno sia piacevole." (I hope your stay is pleasant.) This is a very polite and formal option.
* Informal: "Spero che ti diverti durante il tuo soggiorno." (I hope you have fun during your stay.) This is more suitable for friends or family. Or, even more casually: "Spero che ti piaccia il tuo soggiorno!" (I hope you like your stay!)
* Alternative (for a hotel): "Buon soggiorno!" (Have a good stay!) This is a common and concise phrase used in hotels.
The best translation will depend on the specific situation.