Aerostar pilot reported controlled flight toward terrain event while sightseeing during descent. Pilot responded to onboard warning to avoid terrain and landed uneventfully.

Narrative

Flight from ZZZZ to ZZZ during the afternoon in VMC/daylight hours with clear skies and unrestricted visibility.Relevant facts leading up to the incident are that ZZZZ Center requested a route over the airport (so much for a direct flight) then 'remain on frequency and report 20 miles of the border' which I did. ZZZZ Center then released me at which point I tried to contact ZZZ FSS initially unsuccessfully. When I did reach ZZZ I identified myself as Aerostar level at 8;500 inbound to the USA and looking for the discrete code to cross into the United States. The code was provided along with some other customary data including current conditions at ZZZ airport; the destination airport for US Customs.The VFR intended route of flight from ZZZZ1 commonly taken was to fly essentially north [by] ZZZZ2 (another airport enroute in condition and length to handle my aircraft is necessary); then by ZZZZ3 Airport and intersection to ZZZZZ for a slight right turn setting up the (preferred) left downwind for landing on runway XX at ZZZ.This route is from my experience the safe option if bad weather or mechanical issues should arise as it arguably offers the most options to completing a safe flight and I have used this selection previously for flight from ZZZZ1 to ZZZ as well as from flight to and from ZZZZ3 and ZZZ with intersection ZZZZZ as a waypoint as it routes with the most obstacle clearance from the various mountains and hills to either side of the flight and it also sets up nicely for runway alignment between the two airports as well as easily identifiable landmarks. Intersection ZZZZZ also serves as a good waypoint for numerous other flights I have logged from the east on either side of the border and form the west of the border as it keeps me out of MOA's and especially out of Restricted airspace. In addition the eAIPS filing requires a border crossing point (including time of crossing). With the border crossing approved the remainder of the [flight] continues with the CTAF frequency call to traffic at ZZZZ3 announcing my distance of some XX nm and altitude of 8;500 feet MSL and intention to land on runway XX while listening to weather on the backup frequency in the background as I was now able to receive it. The descent initiated once I had ZZZZ3 airport portside for intersection ZZZZZ and subsequent slight right turn placing me about XX miles from the airport and follow up call over ZZZ; ready set up for the preferred (and recommended) runway XX.Powering back the turbochargers (mechanical system in my model) and reducing power for the descent we also enjoyed the sightseeing as both myself and sole passenger; my wife in the co-pilot seat; looked for places below we had visited. The descent of some 1;500 feet per minute was trimmed and no autopilot was in use. The aircraft has been flown by my for numerous years and is equipped with a Altitude Alerting System; a Radar Altimeter and a GPS with ground proximity capability; including an standard Altimeter and VSI. In addition I had in place a IPhone (dash mounted) with and electronic flight bag installed and IPad capability (not plugged in) during this flight. The descent and sightseeing continued until I observed the second countdown timer triggering the upcoming right turn of some 30-40 degree for the airport; which I initially several seconds later as I continued the descent… now with a 'Pull Up' ground proximity alert also on the display. I arrested the turn and leveled the wings; pulled back on the controls reversing the some 2;000 ft/min descent into a climb until the warning cleared; and returned to the heading leveling off at pattern attitude for the airport. A call to ZZZ FSS to cancel my flight plan as I was coming into the pattern and the usual calls and procedure for landing in sequence from there as the remainder of the flight was uneventful.Despite having numerous devices onboard; I had failed to use them in my favor and as aid to avoid a descent to such low altitude. IPhone with capability to display terrain at my eyelevel as it was in video mode; yes I was filming to add to the distraction; in addition to sightseeing. An I-Pad with similar capabilities; a Radar Altimeter not set; along with an Altitude Alerting device not programmed for airport pattern altitude. While the entire incident likely occurred in foreign airspace I do believe the flying community may benefit from my report as I hope it will. As such contributing factors were the selection of an intersection (ZZZZZ) which appears to be the low point of the area and any of the surrounding terrain in addition to being located at the distraction point of the sightseeing part of the flight. Familiarity with the surroundings from the air and ground and excellent weather helped in lulling away the full use of available resources to maintain proper altitude.Cause: A birthday celebration the evening before with perhaps some sleep deprivation. Suggestion: Perhaps intersection ZZZZZ is not the best choice here as it sits terrain low; is over the town of ZZZ and overhead a major border crossing and port of entry; options are ZZZZZ1 further east and at higher elevation or ZZZZZ2 even further east and an intersection I have used in the past as a gateway arriving from the east; paralleling the border on the USA side to keep me clear of the several Restricted airspace(s) and east of ZZZ [airport]. Use as many tools as possible you have at your disposal indifferent of perceived 'easy flying' conditions. Focus on the flight and leave all other worldly issues on the ground. Don't let passengers aid in your distraction(s); conversations; especially on initial and final stages of a flight as 'it can wait until you are on the ground' to talk about. It's a license to learn; keep learning; which I hope to have accomplished with this lesson in hand. One I hope some of you benefit from and for the majority I hope already know better and use this only to reinforce their sound flying practices.