Spain/Portugal/Gibraltar - 6 hour layover in Lisbon

Arrive from US on a Saturday in May at 8:20 am, depart 2:20 pm (to Amsterdam). How long to clear customs?
Enough time to:
- ride Tram 28
- take Tram 15 to visit the Belem Tower and Jeronimos Monastery
- return to airport and clear security???
Please advise if this is possible and how much time to allot to each part of this adventure.

Arrive from US on a Saturday in May at 8:20 am, depart 2:20 pm (to Amsterdam). How long to clear customs?

0 to clear customs. Presumably your luggage will be checked through, so you won't have customs. Technically they may stop and inspect you, but in practice with just a light carry-on they are unlikely to stop you.

Your wait will be for immigration. If you hold a EU or Swiss passport, the wait will be minimal. If not, it could be a while, perhaps 30 to 45 minutes. On some days of the week, just before 8:20 there are a few Africa and Brazil arrivals that tend to back up immigration.

Enough time to:
- ride Tram 28
- take Tram 15 to visit the Belem Tower and Jeronimos Monastery
- return to airport and clear security???
Please advise if this is possible and how much time to allot to each part of this adventure.

There are often lines to visit Belem Tower and Jeronimos Monastery, especially on a weekend. So even if you get there, there may not be enough time to visit. The Tower is much smaller than the Monastery, so if you try to visit one try the tower. However, tram 15 runs right in front of the Monastery but a bit of a hike from the tower, so it may be a wash. I doubt that visiting the inside of either will be feasible in 6 hours.

To get on either tram, from the airport take the Aerobus (http://www.carris.pt/pt/autocarro/91/descendente/default/) to Praça do Comércio. The 15 leaves right there from Praça do Comércio, whereas the 28 stops at Rua da Conceição, a couple of streets north of that (you will have crossed the 28 tracks a couple of blocks before the Praça do Comércio bus stop). Pick one.

If taking the 28, I suggest taking it towards Graça or Martim Moniz. Some trams go to Graça, others to Martim Moniz (which is after Graça), but in any case just get off at Graça and head back on the 28 going the other way. The ride from Rua da Conceição to Graça should be 10 minutes or less. From Graça, I suggest taking the 28 in the opposite direction, past Rua da Conceição and get off at São Bento (the parliament building). From there walk down towards the river where you will catch the 15.

Take the 15 west towards Algés, get off in front of the Mosteiro dos Jerónimos. It should be about 15 minutes for that ride. On the way back, take the 15 back to Cais do Sodré, where you can connect to the Aerobus back to the airport.

So there you have it. Approximate times:
- wait for the aerobus: up to 20 minutes (it runs every 20 minutes)
- ride the aerobus from the airport to downtown on a saturday: allow 30 minutes
- walk to Rua da Conceição for the 28: 5 minutes
- wait for the 28: 10 minutes (this could be significantly longer is trams are full and you have to see several go by)
- ride the 28 to Graça: 10 minutes
- wait for the 28 back: 10 minutes
- ride the 28 to São Bento: 15 minutes
- walk to the river: 10 minutes
- wait for the 15: 10 minutes
- ride the 15: 15 minutes
- wait for the 15 back: 10 minutes
- ride the 15 back: 20 minutes
- wait for the aerobus: 20 minutes
- ride the aerobus: 30 minutes

You are already at 215 minutes, and all you did was ride back and forth. Add some more time for ooh and aah and gawk at stuff, and you easily are at 4 hours or beyond. Absolutely no time to visit the Tower or Monastery. And all this presumes you know exactly where to go and what to do at each stop. It is doable but very tight with a six-hour layover. Keep a time log and see how you are doing relative to plan, and if needed abort portions of the plan or take a taxi back to the airport.

You will save some time if you take a taxi from Belém direct to the airport, but finding a taxi available may be a challenge depending on the season.

Walking from the Jerónimos Monastery to Belém Tower is a good 10/15 minutes, each way. Taking a cab does not save time here because the cab has to go quite a long way around to get across some railroad tracks that you as a pedestrian can cross using the pedestrian bridge. It will be tough to ride trams and see both.

Money saving tip: the aerobus ticket (€3.50) is good to ride the aerobus plus all Carris buses and trams all day. So save your initial aerobus ticket and it will be good for all those trams and even for the aerobus back to the airport. This is quite a savings since tram rides would be €2,50 each otherwise.

For some ideas, check out this thread: http://www.flyertalk.com/forum/europe/1134837-stop-over-lisbon-any-ideas-how-kill-7-hours.html

You won't have a full day but only 6 hours so choose and pick from there.

Yes, lines at immigration can be quite long. There's sometimes a shortcut line called the priority line, open to the right of the main snaking queue. I'm not suggesting that you use that, but know that it's there ;).

There are a number of regular buses that leave from the airport and you can get a bus+metro (but NOT aerobus) ticket at the post office on the departures level. On saturday your choices will be 22, 44, 745, 783, each of which either goes to the center or connects to the metro (look on carris.pt for more info on that).

Alternatively take the taxi to Belém or the center. I've never NOT seen taxies at the aiprort. Make sure the driver turns on tariff 1, as many LOVE to turn on the "tourist tariff" (tariff 3), which is supposed to be used outside the city if they see that you're not a local. On a saturday morning aerobus or local buses should not get stuck in traffic anywhere.

I think you should choose either Belém or the city center and explore one of them. You can have great pasteis de nata at many bakeries in the center. They're not as good as paisteis de Belém, but that'll give you something to come back for. :)

... and you can get a bus+metro (but NOT aerobus) ticket at the post office on the departures level.

But beware that the Post Office opens at 9. And by "opens" in Portugal that means that at 9 they unlock the door so you can get in. Then they go sit at their desk, turn on the computer, boot up, login, and maybe at 9:10 they will serve you. If you are lucky they won't take a coffee break before it's your turn to be served.

But beware that the Post Office opens at 9. And by "opens" in Portugal that means that at 9 they unlock the door so you can get in. Then they go sit at their desk, turn on the computer, boot up, login, and maybe at 9:10 they will serve you. If you are lucky they won't take a coffee break before it's your turn to be served.

Ah yes, you're right, I forgot that it opens at 9.