Most successful podcasts seem to hit certain niche markets. Traveling generally is not a niche market. You get a popular attraction, say the Eiffel tower, and all the real culture and interesting bits about the area are sucked out of it as everything is focused on making money from willing tourists.

Something I personally would love to do is go to very popular destinations, but ignore the one thing everyone else is going for. For example, go to Las Vegas and stay off of the strip the entire time. There is a lot of fun to be had in the surrounding area, (Baja racing anyone?) that many people never see.

So, what I would suggest is a podcast that explores popular destinations, but shows the almost behind the scenes experiences that can be had.

I think with this approach you may refine the audience a certain amount, to people who really want to learn about different cultures, not just see some tower here and gamble there.

Hope that helps.

First decide if you are going to make a podcast about destinations or experiences. To me, the larger market (and and better commercial application) would be a podcast related to destinations.

For an experiences focused podcast, I believe audio would be the best format. Basically you will gather an audience who wants to here stories, not necessarily an audience who wants travel information. You could build a very active community but I'm not sure how much commercial activity you could generate.

For destinations I believe a video format would work best, however it does not need to be live action video. Narrated photos would work very will with just a minimum of other video if you actually visit the destinations. The video should be quite short, probably less than 15 min, and should contain links to your (or other) website for additional detail. This kind of podcast would really just be intended to drive web traffic and perhaps a travel business.

If you're creating a podcast for others, think about the audience you'd like to reach and what you mean by "travel podcast." If it's a music podcast for travelling listeners, keep it to between 30 and 60 minutes. Most commutes won't be much longer than that, so a longer podcast would be a waste of time to create. If you're talking about a podcast about destinations for travellers, make it long enough to get all the pertinent information about the destination out there but do not pad it with fluff. If it only takes 15 minutes to discuss a destination, it's highlights, and some "must see" areas/activities... make it only 15 minutes. If you have a ridiculous amount of information on a destination, try to limit your podcast to about 30 minutes. Personally, I've found any podcasts that are more than 30 minutes on the same topic are generally either not interesting, or not interesting enough to hold my attention for longer than that.

The length depends entirely on if it is video or audio. Video traditionally works better under 10 minutes (or 15 mins max and I think 5 mins is the best). The only exception is pretty much Diggnation which is very long for video. If you are doing audio, listeners pretty much expect a podcast that is at least an hour long (for a weekly podcast, if you are doing daily, more around 10 minutes).