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
Edit: I like run on sentences...
As a follow-up/slight refocusing: Can one track a change in tourism levels throughout the period? I figure the tourism wouldn't be amazing during the height of Germany's hyperinflation, and obviously tourism would've dropped off during and around WW1 and 2, but if there's any way to track what might be a "standard" rate of tourism for Germany during the period, I could see that being valuable in answering this question.
Follow up: How were Jewish tourists treated?
Followup: How much did the distribution of nationalities among tourists change during that period?
Another follow up, are there any instances of people visiting Germany and being sent to a concentration camp or detained?
A challenge in answering this question for all of Germany is the lack of statistical data for the interwar years. In the German Kaiserreich (1871-1918) the only state with an official tourism Statistic (Landesfremdenverkehrsstatistik) was Bavaria from 1910 onwards. During the Weimar Republic (1918-1933) the other states were also obliged to compile according Statistics. However, according to 1997's "Reisekultur in Deutschland: Von der Weimarer Republik zum Dritten Reich" (Peter J. Brenner et al) it took several years until reliable data was available. The same book also describes the first national tourism Statistics and notes that the Statistisches Reichsamt's figures (quoted on p. 56 from their yearbooks) are initially not representative for Germany as a whole since they are explicitly sampled from merely ten destinations. Only starting in 1929, the yearbook lists data from 2000 municipalities, in 1936 for 3155 municipalities and from 1937 onwards for 4650 municipalities - still a lot less than the total number (~ 75000), but likely covering the relevant tourist destinations.
Also note that Germany hosting the Olympic Games (Summer and Winter) in 1936 will heavily influence data for that year.
That said, the original question can be answered for Bavarian municipalities until the late 1930s. The city of Nuremberg has put some older issues of its Statistisches Jahrbuch (statistical yearbook) online. Taking their figures, ...
in 1919, out of 227967 visitors staying overnight, about 91 % were Germans and 1,2 % were Austrians and Czechoslovakians. (Table 144 and Table 145).
in 1920, out of 239885 visitors staying overnight, about 88 % were Germans and about 2,5 % were Austrians and Czechoslovakians. Four Australians visiting individually, BTW. (Table 144 and Table 145).
in 1928, out of 283824 visitors staying overnight, about 80 % were Germans and around 4 % were Austrians and Czechoslovakians (Table 104).
in 1929, out of 288646 visitors staying overnight, about 79 % were Germans and around 4 % were Austrians and Czechoslovakians (Table 104).
in 1930, out of 290426 visitors staying overnight, about 74 % were Germans and around 4 % were Austrians and Czechoslovakians (Table 104).
in 1934, out of 233410 visitors staying overnight (but excluding 497000 visitors to the Reichsparteitag!), about 83 % were Germans and a bit less than 0,7 % were Austrians (now counted without Czechoslovakia). (Table 86).
in 1935, out of 289704 visitors staying overnight (but excluding 50124 visitors to the Reichsparteitag!), about 86 % were Germans and around 0,8 % were Austrians. (Table 86).
in 1939, out of 438539 visitors staying overnight, about 92 % were from places in the Deutsches Reich (including Austria). The high number of visitors might include visitors for the scheduled Reichsparteitag which was cancelled on short notice. (Table 85).
in 1940, out of 263581 visitors staying overnight, about 98,6 % were from places in the Deutsches Reich (including Austria). (Table 85).
Another follow-up: Can anyone elaborate on W.E.B. DuBois and Jesse Jackson's Owens' experiences in NS Germany?
In a similar question, were us tourists allowed to visit Germany during ww2?