I see that Maine has Constitutional Carry.  How does that work for an out of stater?  I'll be going to Acadia National Park soon and would like to bring at least a pistol if I can.  Maine used to honor Pa's permit, but with Constitutional Carry our state revoked reciprocity.

https://www.maine.gov/dps/msp/licenses-permits/concealed-carry-maine

Concealed carry without a permit is limited to people who are 21 or older, with the following exception:  If a person is 18 years of age or older, and is on active duty in the Armed Forces of the United States or the National Guard, or has been honorably discharged from the Armed Forces or the National Guard, and is not otherwise prohibited from carrying a firearm, the person may carry a concealed handgun.  A person who is 18-20 years old and without the referenced military qualifications must have a permit to carry concealed.  The law applies to both residents of Maine and non-residents.

The law does not otherwise change where a person may carry or who may possess a firearm.  It will still be illegal to possess a firearm in the following places, with some very limited exceptions:

Courthouses (17-A M.R.S.   1058)
State Parks (12 M.R.S.   1803(6), (7) and Bureau of Parks and Lands Rules Chapter 1)
Acadia National Park (12 M.R.S.   756)
Schools (20-A M.R.S.    6552)
Federal buildings (18 U.S.C.   930)
State Capitol area (25 M.R.S.   2904 & DPS Rule Chapter 41)
Private property when prohibited by the property owner
Establishments licensed for on-premises consumption of liquor, if the premises are posted.  Note that even if there is no posted prohibition, it is illegal to carry on these premises while under the influence of intoxicating liquor or drugs. (17-A M.R.S.  1057)
Wildlife Sanctuaries (as listed in 12 M.R.S.   12707)
Labor disputes and strikes (32 M.R.S.   9412(5))
Baxter State Park (as prohibited by Rules)
Allagash Wilderness Waterway (as prohibited by rules)
There will be some circumstances in which an optional handgun permit will authorize the permittee to carry in certain locations or during an activity when an unpermitted person could not:

Acadia National Park (Maine Permit required; 12 M.R.S.  756) NOTE: Pursuant to 25 M.R.S. 2001-A (2)(F), Maine will recognize a concealed handgun permit issued by another state to its resident if that state recognizes Maine's resident concealed handgun permits. A resident permit from that state is valid for concealed carry of a handgun within Acadia National Park
State Parks (Permit required; open carry not permitted; 12 M.R.S.   1803(7))
Regular archery hunting-deer only  (Permit required; 12 MRS   11403)
Employees' vehicles on work premises (Permit required; vehicle must be locked and firearm must not be visible; 26 M.R.S.  600)
If an individual is carrying a concealed handgun without a permit, he/she has a duty, when coming into contact with any law enforcement officer during a routine stop, detention or arrest, to immediately inform the law enforcement officer that the individual is carrying a concealed handgun.

Thank you.

@JKrammes

Same.

How was your experience?

Good.  No issues.  Love Acadia and the surrounding area.

To be clear.  We did not stay in Acadia, and I did not carry in the park.

@JKrammes

We won’t be staying in Acadia either. Why can’t you carry there? Isn’t it a national park? What makes it different than every other national park that you can carry in, sans the visitor centers and other buildings, etc.?

ETA: I have a concealed handgun permit from a state that recognizes Maine and has reciprocity, so perhaps it’s a moot point and I can carry within the park?

Because of this clause.  My state no longer recognizes Maine because they are Constitutional carry.  I just did't want to push it.
Acadia National Park (Maine Permit required; 12 M.R.S.  756) NOTE: Pursuant to 25 M.R.S. 2001-A (2)(F), Maine will recognize a concealed handgun permit issued by another state to its resident if that state recognizes Maine's resident concealed handgun permits. A resident permit from that state is valid for concealed carry of a handgun within Acadia National Park
State Parks (Permit required; open carry not permitted; 12 M.R.S.   1803(7))
Regular archery hunting-deer only  (Permit required; 12 MRS   11403)
Employees' vehicles on work premises (Permit required; vehicle must be locked and firearm must not be visible; 26 M.R.S.  600)
If an individual is carrying a concealed handgun without a permit, he/she has a duty, when coming into contact with any law enforcement officer during a routine stop, detention or arrest, to immediately inform the law enforcement officer that the individual is carrying a concealed handgun.