Should I book a round-trip ticket to Lima or a multi-city flight?

If you are doing a standard loop through the Sacred Valley, a round-trip to Lima is almost always cheaper. If you have limited time, pay the premium for a multi-city flight (into Lima, out of Cusco) to avoid backtracking.

Is it safe to book with third-party sites like Kiwi or Expedia?

It is safer to book directly with the airline. If your flight is canceled or delayed, third-party sites make it nearly impossible to get a refund or rebooked.

How to Book Flights to Peru

To get the best price, book your international flight to Lima at least 3 months in advance and use a flight aggregator to track prices. Always ensure your arrival is at Jorge Chávez International Airport (LIM), the only major international gateway for the country.

Set up a price alert. Use Google Flights to track routes from your home city to LIM. Set the alert 4 months before your intended travel dates to capture the price drop that typically happens 90 days out.
Choose your carrier wisely. LATAM is the most reliable carrier for domestic connections within Peru. If you book an international leg with a partner airline (like Delta or American), ensure it is under a single ticket (PNR) so you are protected if the first flight is delayed.
Check visa-related entry requirements. Before hitting 'purchase,' verify your passport validity. Peru requires your passport to be valid for at least 6 months beyond your date of departure from the country.
Book domestic legs separately if needed. If you are flying to Cusco or Arequipa, it is often cheaper to book a separate flight from Lima once you have secured your international ticket. Use the Peruvian version of the airline websites to avoid 'tourist pricing' on domestic legs.

Should I book a round-trip ticket to Lima or a multi-city flight?: If you are doing a standard loop through the Sacred Valley, a round-trip to Lima is almost always cheaper. If you have limited time, pay the premium for a multi-city flight (into Lima, out of Cusco) to avoid backtracking.
Is it safe to book with third-party sites like Kiwi or Expedia?: It is safer to book directly with the airline. If your flight is canceled or delayed, third-party sites make it nearly impossible to get a refund or rebooked.