When it comes to crossing international frontiers, there's one travel document that opens more doors than any other.
And it isn't a U.S. passport.
German citizens, it seems, have the potential for the greatest mobility in the travel world.
With a German passport, travelers can enter 177 out of 218 countries and territories without a visa, according to the 2016 Visa Restrictions Index.
The list, compiled annually since 2006 by London-based consulting firm Henley and Partners and the International Air Transport Association, ranks nations by how freely their citizens, unencumbered by immigration red tape, can explore the planet.
This year, it shows that citizenship of a superpower doesn't carry the clout it once did.
The United States, which ranked first in 2014 and 2015, has now dropped to fourth place.
Immediately behind Germany, holding its position as runner-up for the second year running, is Sweden with visa-free access to 176 countries.
Finland, France, Italy, Spain, and the United Kingdom -- which had topped the list since 2013 -- are now tied for third place, making Northern and Western European citizens the most privileged in international travel.
Japan and South Korea were also among the group in the top three in 2014 and 2015, but have slid down to fifth and sixth place respectively this year.
Belgium, Denmark and Netherlands stand alongside the U.S. in fourth.
At the bottom of the list, labeled countries with the "worst passports," are Afghanistan, at 104, followed by Pakistan, Iraq, Somalia, and Syria.
With cumulative data from 11 years, the site allows users to compare multiple countries' scores on a list, a color-coded world map, and a graph, or chart a country's progress regarding visa policies over the decade.
Henley and Partners, a firm specializing in immigration and citizenship services, explains that visa requirements "reflect strongly" on countries' relationships.
"Criteria that a country will consider when considering giving visa-free access to citizens of another country may include diplomatic relationships between the countries, reciprocal visa arrangements, security risks, or risks of violation of visa terms," a representative of Henley and Partners tells CNN.
Observing that no country has dropped more than three places while some made huge leaps, the company concludes that freedom of movement, in terms of "visa-free access," is generally improving around the world.
East Timor, which gained independence in 1999 and signed a mutual visa-waiver agreement with the EU in May of 2015, made the steepest climb of 33 places to land at 57. Meanwhile, Colombia, at 50th, moved up 25 spots.
Hong Kong, a special administrative region of China, fell from 16th to 20th place.
A surge in country wealth that allows citizens to flash their tourism cash may also mean a warmer welcome from other destinations.
China is now at 87, tied with Cambodia, having risen from 93rd place in 2015 after countries like Japan, South Korea and the United States relaxed visa restrictions for Chinese tourists.
It's now above Chad and below Sierra Leone.
The United Kingdom and Australia have also announced plans to further ease requirements to attract Chinese tourists.
The large disparity between different citizens' travel mobilities is striking.
Wealthy countries continue to afford citizens free movements and opportunities around the world, while countries torn by war and conflict remain stuck on the bottom rung of the list.
Afghanistan has come last since 2010.
Those uprooted by violence and fleeing wars or economic desperation have also been contributing to the rising tide of refugees and migrants entering Europe.
Retaining the Index's top spot from the last two years, Germany received more asylum seekers than any other industrialized country in 2014, according to the United Nations.
World's best passports (by number of countries granting visa-free access)
1) Germany -- 177
2) Sweden -- 176
3) Finland, France, Italy, Spain, UK -- 175
4) Belgium, Denmark, Netherlands, U.S. -- 174
5) Austria, Japan, Singapore -- 173
6) Canada, Ireland, Luxembourg, Norway, Portugal, South Korea, Switzerland -- 172
7) Greece, New Zealand -- 171
8) Australia -- 169
9) Malta -- 168
10) Czech Republic, Hungary, Iceland -- 167
11) Slovakia -- 165
12) Liechtenstein, Malaysia, Slovenia -- 164
13) Latvia -- 163
14) Estonia, Lithuania -- 162
15) Poland -- 161
16) Monaco -- 160
17) Cyprus -- 159
18) San Marino -- 156
19) Chile -- 155
20) Hong Kong -- 154
World's worst passports
94) Liberia -- 43
95) Burundi, North Korea, Myanmar -- 42
96) Bangladesh, Democratic Republic of Congo, Lebanon, Sri Lanka -- 39
97) Kosovo, South Sudan, Yemen -- 38
98) Eritrea, Ethiopia, Iran, Nepal, Palestinian Territory, Sudan -- 37
99) Libya -- 36
100) Syria -- 32
101) Somalia -- 31
102) Iraq -- 30
103) Pakistan -- 29
104) Afghanistan -- 25