Located in the central part of the archipelago. Baltra is the only island that is not part of the national park, but is a military base and the airport.
Most people arriving to the Galapagos will have Baltra included on their itinerary, as Baltra is the main airport servicing the Galapagos Islands it is also the airport servicing the island of Santa Cruz.
Flights arriving daily from continental Ecuador arriving from either Quito or Guayaquil. Airlines providing service include:
Arriving at Baltra passengers pass through the national park queue (and pay a $100 park entrance fee). They then proceed to the luggage claim area to the right. Luggage handling is manual and slow, so expect to wait a bit before being allowed to enter the luggage claim area. Then look forward to a scrum as passengers locate their baggage. After finding your bags you queue for a check of your luggage and claim ticket, and then you exit the airport.
There are two sets of buses taking people from the airport. One set takes people who are boarding a cruise, the other takes passengers to the Itabaca channel between the island of Balta and the island of Santa Cruz (and the town of Puerto Ayora). See getting into Puerto Ayora for instructions from that point.
Inter-island flights  are available to both Isabela and San Cristobal islands. Flights usually range $160-$170 each way or $260 round trip.
The airport offers souvenir shops, a restaurant, telephones and internet access. Land Iguanas, Darwin Finch and other lava lizards are all frequently seen at the airport.
Leaving the airport, you will travel by bus passing the remains of the old US Air force base set up in World War II to protect the Panama Canal.
For many travelers this will be your only opportunity to purchase post cards prior to visiting the Post Barrel on Floreana
Cruise and tour companies pick up their guests at Baltra airport, it is usually the start or the end of cruise and hotel based tour packages. One of many companies starting its trips at Baltra is Voyagers - https://www.voyagers.travel/galapagos-island-baltra/
The closest islands to Baltra are: