First time trip to Switzerland from Italy

I am very familiar with the trenitalia train system, can you really just go on any train with the STP? I won't need reservations or validating?

If you buy your STP (Swiss Travel Pass) in Luzern, you will specify the travel period and it will be on the pass. Then, when the conductor comes by to check tickets, just show your pass and ID (passport), and that is it. The only trains that need reservations are the "named" tourist trains with panorama cars like the Glacier Express or Bernina Express.

Interlaken and Lauterbrunnen are different animals, only 20 minutes apart by trains every hour. Interlaken is a large town between two big lakes. Lauterbrunnen is a smaller town between two large mountains. They are on the way from Luzern to Zermatt, so rather than double back to Luzern, stay there for at least one night on the way.

If you return to Milan from Zermatt on the EC train from Visp or Brig, the Italian section does require reservations, which will be included in the ticket. If the STP is still active, the Swiss portion to Domodossola will be covered by the pass.

Swiss Railways and Italian railways have totally different philosophies for their ticketing systems. This confuses people used to one system when they encounter the other.

The Swiss operate a "turn-up-and-go" system. Every rail route has at least one train per hour (often two), at the same minutes past every hour, and designed to connect at all the interchange points. It is common when a train pulls into a station to see connecting trains and buses lined up waiting for connecting passengers, timed to depart just after the train arrives.
Tickets are valid on any train (on the date printed on the ticket), like Italian regional tickets but there is no validation. Reservation is not needed and in most cases not possible.

So yes, once you have your Swiss Travel Pass, you just walk up to the station (or bus stop), wait for the next train and get on. It is that easy.

For Luzern, it is a town and you would need to get out of town to find walking. The lake boats are good to get you to such places. For Lauterbrunnen the walking starts outside your door.

If arriving from Milan, your Swiss Pass is valid from either Domodossola or Chiasso, depending on route taken. You would need to buy an Italian ticket from Milan to there.
Here is a Swiss rail map showing where your pass is valid. You should get a copy of this with your pass: https://www.sbb.ch/content/dam/sbb/de/pdf/freizeit-ferien/ferien-kurztrips-schweiz/internationale-gaeste/uebersichtskarte_synoptic_map_2017_low.pdf

After many trips to Switzerland, we find ourselves always drawn back to the Lauterbrunnen Valley. We are "easy hikers" and there are tons of easy hikes in the area, surrounded by magnificent peaks. It is, to us, much lovelier and with better walking than Luzern. (We did not really care for Luzern and even for Switzerland it was VERY expensive.) Plus a day trip between the two involves 3-hour train rides each way!

I would stay in Lauterbrunnen for all 5 nights. We've been to Zermatt and it is lovely but there are two challenges: the "walking" is really more "hiking" and if you are only there two nights, what if the weather is bad on your ONE DAY? Yikes!

but the train from Milan to Lauterbrunnen is several hours with multiple changes.

It's not that bad. In fact, it is fun to see how the transportation system works. Milan to Spiez, then Spiez to Interlaken Ost, followed by Interlaken Ost to Lauterbrunnen. You're done. Stay there in the valley and to both sides for walking. Consider a Berner Oberland Regional Pass for the lifts and mountain trains instead of an STP. You might benefit from the combination of Half-Fare Card and a BO Reg Pass.

thank you all for the great ideas, love this forum and its great contributors!

Don’t let the gondola ride stop you from staying in Murren or Gimmelwald. It’s quite easy and the gondolas are quite large and I find them relatively smooth riding. I do prefer to stay up on top rather than down in the valley. Plenty of easy walks.

FYI the train from Interlaken Ost to Lauterbrunnen splits up. Make sure you are in a car marked for Lauterbrunnen.

sorry...one more question. Am I reading Trenitalia's site correctly that I can go from Milano Centrale to Luzern with an EC ticket for 29 E in advance at 10:15? I don't have to stop at Domodossola first and change trains? If I go onto the DB website, it shows a different time schedule. I will be coming from Firenze to Milano to jump on the train to Luzern (I know it will be a long day but exciting with great views).

Marie, Yes, there is a 10:15 train from Milano to Luzern. I just looked it up on the SBB website: https://www.sbb.ch/en
€29 is a good price. This train stops at the following stations:

Milano Centrale dep 10:15 EC158, End destination Basel SBB
Como S. Giovanni dep 11:03
Chiasso dep 11:15
Lugano dep 11:43
Bellinzona dep 12:13
Arth-Goldau dep 13:14
Luzern arr 13:41

Note this crosses the border at Chiasso, NOT Domodossola. If you were going to Interlaken etc., then the route is via Domodossola. But, in neither case do you need to get off the train at the border, it is just a stop and a crew change.

There are lots of other options, 09:25, 10:15, 11:25, 13:25 etc. These other options require a change of trains at Arth-Goldau, no problem as the two trains sit at opposite sides of the same platform and doesn't take any longer.
Note, the Trenitalia (Italian Railways site) does not show Swiss internal trains, so it does not show the options where you change at Arth-Goldau. The SBB site does, so that is the better one to use.

By the same token, you can travel from Milan to Spiez, Switzerland without changing trains for good prices with advance nonrefundable fares ("Smart" fares) on EC trains. Spiez is just a hop skip and a jump from Interlaken and Lauterbrunnen.

Appreciate the follow up and advice! Really looking forward to visiting Switzerland as well as Italy again. Grazie tante!

Lauterbrunnen is 25 times better than Interlaken for a base. I've stayed in both.
If you like (easy to moderate) hiking, there are at least a dozen great trails in the Lauterbrunnen area.
A few of the higher trails may still have snow on them in May, but the Tourist Info in Laut. will know.

Here are a bunch, all great, though 7,8,9 may be snow-covered in May.

1. Mannlichen to Kleine Scheidegg (and even further to Wengernalp)
2. Grutschalp to Murren
3. Top of Almendhubel (via funicular up from Murren), go right, generally heading above Winteregg, then clockwise back down to Murren
4. Top of Almendhubel, go left, towards Schiltalp, then Spielbodenalp, then to Murren
5. Murren to Sprutz Falls, under the falls, up the opposite side to Spielbodenalp, then back to Murren
6. Lauterbrunnen to Trummelbach Falls walk through the valley
7. Schynige Platte to First (6 hrs, but great!)
8. First to Bachalpsee and return (shorter version of #7)
9. First to Grosse Scheidegg and bus back to Grindelwald
10. Grindelwald, cable car to Pfingstegg (take the Rodelbahn luge ride there!), hike to Berghaus Baregg
11. Circular trail starting and ending at Schynige Platte.

These 2 maps will help:
https://terrelledwards.files.wordpress.com/2012/01/hikingmap1-3-2.jpg
http://ontheworldmap.com/switzerland/ski/jungfrau/jungfrau-summer-map.jpg

@shoe
Thank you so much for the trail advise. Where did you stay in the valley? We will be doing a day trip to Luzern and Zermott, but decided to base in Lauterbrunnen area. Thanks

Marie,
We love this apartment in Lauterbrunnen. 1 km walk to the train, but right on the Post Bus route. I like to have an apartment when we stay somewhere 4 nights or more, and especially in Switzerland so I can cook a little as restaurants are so expensive!