even the monkeys will steal your stuff from the beach

there bring nothing of value.

tripadvisor.com/members/natureguide

will show you a tonne more than you can see yourself.

insuremytrip.com always wise park closed Monday

Have fun,

I wouldn't leave anything unattended. I'd also really recommend getting a guide. We would have walked right past several things without ours - a sloth, bats, cool insects, etc. You'll see the big stuff like monkeys but probably a lot more with a guide.

I'd also recommend a guide. I've found they are much better trained at finding wildlife compared to the average person!

The nature guide at Arenas del Mar, Ersel, is great (of course I am assuming he is still there). He may be able to go with you or recommend someone. If you like birds I suggest taking his morning bird tour, I think we saw something like 25 in the space of the short-ish tour. I think you will find that the wildlife ignore park boundaries, and
at Arenas del Mar you are going to see most of the same common wildlife as at Manuel Antonio, ie sloths, howler monkeys, agoutis, basilisk lizards, iguanas, white face capuchin, and possibly the squirrel monkeys (they come thru at certain times, ask the staff what their schedule is).

The beach at MA is very sheltered but the monkeys will grab your bag. So someone is going to have to stay on the beach and watch it for you. I was at AdM for nearly a week and went to Manuel Antonio Park once. I didn't find it was worth a return.