The online information on hiking in English is limited. A visit of the local tourist offices will be of benefit on this. They have maps and better printed tour descriptions.
Some hiking routes on the Oberstdorf website in English
The two main regional tourist websites are however since their last redesign only in German. Strange that it is often easier to find printed information in English than online.
A brochure "Hiking with trains and buses" (in German) with 50 route suggestions
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There is no real alternative. The Oberstdorf AllgäuWalserCard covers only the town buses. Not the buses to many nice hikes around Oberstdorf. Or to the Kleinwalsertal - a valley in Austria which can be however only reached from Oberstdorf. Many nice walking options there as well.
bus timetables Oberstdorf / Kleinwalsertal
train and bus timetables for the Southern Upper Allgäu
The most interesting town in the Southern Upper Allgäu is Immenstadt
There are also a number of castles and castle ruins in the Allgäu
The Urlaubskarte is also of use to some interesting places outside the Southern Upper Allgäu
There is a daily pair of buses Mo-Sa from Oberstdorf to Füssen / Hohenschwangau (Neuschwanstein castle) and to Lindau (Lake Constance)
Oberstdorf - Füssen - Hohenschwangau is fully covered. Between Füssen and Hohenschwangau you can even use all buses.
It is essential to reserve tickets for the castles if you want to visit them (inside).
For Oberstdorf - Lindau you have to pay a supplement of EUR 4.
To Kempten you can use the trains - you just need an additional ticket from Martinszell to Kempten (EUR 2,30 pp). You can buy this ticket already at Oberstdorf.