If you only visit one other island during a stay on Santa Cruz, it’d make it Isabela. Regardless of the two hour speed boat journey ($30 each way), which left everyone looking a bit green, the arrival at the port was perhaps where we saw the most wildlife while in the Galapagos.
When we pulled up we saw penguins, pelicans, sea lions and various other birds; of which I do not know the names. We spent a good 20 minutes or so watching the sea lions clamber up a ramp and on to a bench where it fell asleep, whilst the penguins dove into the sea and fought over fish.
We were only on Isabela for the day (about 5 hours due to the time the boats leave). I would definitely recommend staying a night on the island to truly get to see all it has to offer.
We headed straight for the giant tortoise breeding centre, which is a lot better than the Charles Darwin centre in Santa Cruz: it’s bigger and has more information about what the centre does. There were tortoises in all sizes; from fit in the palm of your hand babies to, would have to get a crane to move them adults.
We also had time to walk along the beach where marine iguanas crept up behind us and posed for pictures.
We’d read that you could get to Los Tintorreas, a very good snorkelling spot, by yourselves, this turned out not to be the case and with limited time we couldn’t snorkel there. Instead I swam with penguins, sea lions and fish just by the port. A pretty good second option!