Having written on the topic of forreign tourism before, I'll reproduce that here as it may be of interest, although more can always be said.

Nazi-era Germany wasn't necessarily destination number one for foreigners looking to travel abroad, but that isn't to say it wasn't seeing any visitors, and during the 1930s, Germany wanted to encourage people to see it as a travel destination for both economic and propagandist reasons. the push came both from private, industry related organizations such as well as government related groups, one of the big ones being the Reichsbahnzentrale für den Deutschen Reiseverkehr (German Railroads Information Office, or RDV), which was one of the biggest initiatives for promotion of Germany as a vacation destination, which took up the vast majority of its advertisement focus. They ran 31 offices in 26 countries by 1938, and coordinated from its headquarters in Berlin. The aim of the RDV in its promotions was to serve state needs, not only bringing in foreign currency from visitors, but also attempting to create more positive images of Hitler's Germany for people, even if they were unable to follow through with the journeys the RDV was selling.

The image that the RDV projected was one heavily laced with propaganda. They billed Germany as a modern, attractive, cultural destination, but heavily played up "how Germany is going ahead: no unemployment, production at peak levels, social security, gigantic projects for industrial development, economic planning, organized efficiency, a dynamic will of pulling together – a happy, energetic people who gladly share their achievements with you" to quote one ad. The low cost of Germany as a destination was also a popular draw that the RDV played up, a favorable exchange rate for most foreign visitors allowing for the country to be billed as a good destination for those on a budget.

To focus on the USA, the RDV had an annual budget of 470,000 RM which were spent on initiatives such as newspaper advertisements, promotional films, and informational handouts for travel agencies, highlighting and promoting different destinations of interest in Germany and various events being held through the year that might draw people. They also did 'cultural' promotions with museums and schools. Prospective travelers could reach out to the RDV office and receive sample itineraries to help them plan their trip, as well as informational packets to guide them on various things they would need to be aware of. Although it of course doesn't mean every single person ended up going through with a trip, the RDV was receiving anywhere from 65,000 to 150,000 such inquiries a year during the 1930s, which can help give some idea of the level of interest for travel to Germany from the USA during the decade. The campaign was evidently successful too, and authorities recorded that from 1934 to 1937, numbers of American tourists had doubled. Interestingly, even after war broke out in 1939, the RDV continued to operate in the US, working to signal German confidence in a speedy victory and resumption of travel in the near future, nothing more than thinly veiled propaganda at that point in time - to the ire of many - but it wouldn't be closed down by the US until June of 1941 (offices in neutral and Axis countries would remain open beyond that point).

All in all, the push for foreign tourists seems to have been a successful one. from 1933 to 1935, German authorities claimed that foreign tourism increased 260 percent. Although as with any numbers from the Nazi government, it must be taken with a grain of salt as to its precise accuracy, the numbers certainly were going up. To quote from Semmens' "Seeing Hitler's Germany", from which I've been drawing on here, she provides a brief overview of the numbers for the middle of the decade:

The Olympic Games marked a banner year in international tourism and Berlin was not the only city to benefit. That summer, 1.2 million foreigners, about 15 per cent of all registered visitors, arrived in Germany, an increase of 55 per cent over the summer of 1935. Thuringia alone witnessed a 61.3 per cent rise in visitors from abroad.77 But the Olympic year merely presaged what was to come. Berlin welcomed almost 56,000 more foreigners in 1937 than it had in 1936.

Looking at the entire initiative, it seems to have been on the whole successful in the goals Germany wanted. While the rising amount of tourist traffic to Germany should be understood as part of the larger international picture which "saw a continual increase in leisure travel after the Great War", the initiatives by the German government specifically played an undoubted part in seeing the country, specifically, chosen as a destination out of other options. And although not every visitor of course was swayed and instead left with sour impressions of the Nazi movement and the changes it had wrought, most visitors seem to have left the country for home with thoroughly positive impressions of what they had seen, extolling the "pleasant normality", a small victory for the propagandist aims of the tourist initiative as a whole, although of course hardly enough to sway international opinion in the end.

All cited from "Seeing Hitler's Germany: Tourism in the Third Reich" by Kristin Semmens. Specifically see Ch. 6 "International Tourism" pp. 129-153

You might be interested in reading A Time Of Gifts, by Patrick Leigh Fermor. It's a primary source memoir written by a young Brit who, after (if memory serves, it's been a minute since I read this) dropping out of Oxford, decides on a romantic whim to walk on foot all the way through Europe -- getting to the Continent by boat, of course -- to Istanbul. In, like, 1934. He spends a lot of the book in Nazi Germany, and almost all of his journey is through areas that would soon be Nazi-occupied. Along the way, he mostly either stays with affluent European families via his social connections or falls upon the locals in whatever village he's passing through. He meets lots of Nazi sympathizers and many people who are otherwise not political but, surely, within a few years, would have been swept into the Nazi orbit. (I haven't read up on his more significant acquaintances and what specifically happened to them in the war.)

Of interest here is the fact that Fermor was not in any way an official guest of high ranking Nazi officials. The nation of Germany wouldn't have cared that he was a tourist there any more than 2018 Germany would care if you took one of those Viking River Cruises up the Rhine. He was just a guy who had a harebrained scheme and ended up in Nazi Germany. The UK and Germany weren't enemies yet, and while I'm sure his friends and family back home thought the whole thing was a ridiculous fantasy, there was no real bar to him doing this. As he walks from village to village through Germany, he is greeted warmly by locals and soon finds himself basically on the German "tourist trail", walking the same paths that all kinds of tourists have taken for decades before him. Nobody thinks it is unusual or a bad thing that he is there.

It should be noted that (as far as anyone knows?) this wasn't espionage or any kind of "the other side visiting as a ruse". He was just some guy. He was also white, British, Christian, and I believe he had studied German in school and had connections on the continent. This was also, again, before the war per se and definitely before the "Final Solution" or anything like that.

EDIT: I feel I should also stress that Fermor was not, himself, a Nazi sympathizer and ended up fighting on the Allied side during the war. He also famously lived undercover for 2 years as part of the Cretan anti-fascist resistance and was instrumental in the capture of an important Nazi commander. In part using knowledge that he had gathered on his travels before the war.