Don't buy tickets in advance. When you get to the station (arrive early in case you run into any problems), use the kiosk to print tickets. The policemen in the station are a wonderful resource if you need any help.

Not to my knowledge.

I think that Leeann is right. Transfers are quite easy.

Hello as I recall it is a very tiny town not a big metropolitan hub. There may also be a bus or you could Uber quite reasonably. There were not a lot of train options.

They do run regularly but please check the local websites, we did not and found out at the time we were needing them they were close to strike action which caused delays. I dot know if this is resolved. One day the kisoks were all down no way to pay even staff couldnt help us. You take a screenshot of the kiosk screen that shows their systems are down carry this with you if an inspector gets on the train, you will not have a fine then. We were able to pay when we got off the train instead of on we pirchased a round trip ticket. The systems when up were only partially so the credit card portion was still having problems. We had to have exact change, yes change no paper notes. We jad to ask local businesses for change to feed the machine for the tickets, crazy but true be prepared. The 3 days we travelled the kiosks were down more than up rather than abandon your plans be prepared for this.

サン・ラザール駅は、パリ市内の中心部に位置しますので、デパートやスーパーなどがあり、買い物客が大勢います。もちろん、スリには注意は必要ですが、比較的治安は良いと思います。私は、駅前のホテルに５泊しましたが、夜外出しても怖いと思ったことはありませんでした。むしろ、ルーブル近くのメトロの方が治安は悪いと思います。（そのメトロでもスリに注意程度です）

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