Wengen is one part of a region called the Jungfrauregion.  The best day trips in the area are those to the other Jungfrauregion areas ( http://en.wikipedia.org/wiki/Jungfrau... ). Those regions include several small towns (with populations under fifty) as well as the larger locations of Grindelwald, Murren, Lauterbrunnen, Interlaken, and Unterseen.

Lauterbrunnen is the location which nearly all visitors will explore because this is where travelers arrive in the area most frequently.  Interlake is a favorite town where travelers frequently go to experience horse-drawn carriage tours of the area.

Favorites of the smaller towns in the region include Spiez and Thun.  Spiez is most commonly visited for its vineyards and Thun is most well known for its local market.

Specific locations (other than the general cities of the Jungfrauregion) which make excellent spots for day trips include the Trummelbach and Giessbach Waterfalls and Blausee Lake .  The Trummelbach Waterfalls are glacier waterfalls which can be seen from within the mountain from which they fall.  This is an amazing sight and one which should not be missed.  The Giessbach Waterfalls are less intense but offer a more peaceful day trip which includes boating and swimming.  The lake is also a great place for boating but is most often used for fishing trips.